Kierkegaard is considered by some modern Theologians to be the "Father of Existentialism". Because of his influence and in spite of it, others only consider either Martin Heidegger or Jean-Paul Sartre to be the actual "Father of Existentialism". Kierkegaard predicted his posthumous fame, and foresaw that his work would become the subject of intense study and research. In 1784 Immanuel Kant, many years before Kierkegaard, challenged the thinkers of Europe to think for themselves in a manner suggestive of Kierkegaard's philosophy in the nineteenth century. In 1851 Arthur Schopenhauer said the same as Kierkegaard had said about the lack of realism in the reading public in Either/Or Part I and Prefaces. In 1854 Søren Kierkegaard wrote a note to "My Reader" of a similar nature.

Kierkegaard believed "each generation has its own task and need not trouble itself unduly by being everything to previous and succeeding generations". In an earlier book he had said, "to a certain degree every generation and every individual begins his life from the beginning", and in another, "no generation has learned to love from another, no generation is able to begin at any other point than the beginning", "no generation learns the essentially human from a previous one." He was against the Hegelian idea of mediation because it introduces a "third term" that comes between the single individual and the object of Desire. Kierkegaard asked if logic ends in actuality, can a person logically prove God's existence? Logic says no. Then he turns from logic to ethics and finds that Hegelian philosophy is negative rather than positive. This "third term" isn't mediation, it's the choice to love or not, to hope or not. It's the choice between the possibility of the "temporal and the eternal", "mistrust and belief, and deception and truth", "subjective and objective". These are the "magnitudes" of choice. He always stressed deliberation and choice in his writings and wrote against comparison. This is how Kant put it in 1786 and Kierkegaard put it in 1847:

Hans Martensen was the subject of a Danish article, Dr. S. Kierkegaard against Dr. H. Martensen By Hans Peter Kofoed-Hansen (1813–1893) that was published in 1856 (untranslated) and Martensen mentioned him extensively in Christian Ethics, published in 1871. "Kierkegaard's assertion is therefore perfectly justifiable, that with the category of "the individual" the cause of Christianity must stand and fall; that, without this category, Pantheism had conquered unconditionally. From this, at a glance, it may be seen that Kierkegaard ought to have made Common cause with those philosophic and theological Writers who specially desired to promote the principle of Personality as opposed to Pantheism. This is, however, far from the case. For those views which upheld the category of existence and personality, in opposition to this abstract idealism, did not do this in the sense of an either—or, but in that of a both—and. They strove to establish the unity of existence and idea, which may be specially seen from the fact that they desired system and totality. Martensen accused Kierkegaard and Alex Andre Vinet of not giving society its due. He said both of them put the individual above society, and in so doing, above the Church." Another early critic was Magnús Eiríksson who criticized Martensen and wanted Kierkegaard as his ally in his fight against speculative theology.

From 1821 to 1830 Kierkegaard attended the School of Civic Virtue, Østre Borgerdyd Gymnasium, when the school was situated in Klarebodeme, where he studied Latin and history among other subjects. He went on to study theology at the University of Copenhagen. He had little interest in historical works, philosophy dissatisfied him, and he couldn't see "dedicating himself to Speculation". He said, "What I really need to do is to get clear about "what am I to do", not what I must know." He wanted to "lead a completely human life and not merely one of knowledge". Kierkegaard didn't want to be a Philosopher in the traditional or Hegelian sense and he didn't want to preach a Christianity that was an illusion. "But he had learned from his father that one can do what one wills, and his father's life had not discredited this theory."

Copenhagen in the 1830s and 1840s had crooked streets where carriages rarely went. Kierkegaard loved to walk them. In 1848, Kierkegaard wrote, "I had real Christian satisfaction in the thought that, if there were no other, there was definitely one man in Copenhagen whom every poor person could freely accost and converse with on the street; that, if there were no other, there was one man who, whatever the society he most commonly frequented, did not shun contact with the poor, but greeted every maidservant he was acquainted with, every manservant, every Common laborer." Our Lady's Church was at one end of the city, where Bishop Mynster preached the Gospel. At the other end was the Royal Theatre where Fru Heiberg performed.

Kierkegaard's mother "was a nice little woman with an even and happy disposition," according to a grandchild's description. She was never mentioned in Kierkegaard's works. Ane died on 31 July 1834, age 66, possibly from typhus. His father died on 8 August 1838, age 82. On 11 August, Kierkegaard wrote: "My father died on Wednesday (the 8th) at 2:00 a.m. I so deeply desired that he might have lived a few years more... Right now I feel there is only one person (E. Boesen) with whom I can really talk about him. He was a 'faithful friend.'" Troels Frederik Lund, his nephew, was instrumental in providing biographers with much information regarding Søren Kierkegaard. Lund was a good friend of Georg Brandes and Julius Lange.

Kierkegaard's journals were the source of many aphorisms credited to the Philosopher. The following passage, from 1 August 1835, is perhaps his most oft-quoted aphorism and a key quote for existentialist studies:

One of the first physical descriptions of Kierkegaard comes from an attendee, Hans Brøchner, at his brother Peter's wedding party in 1836: "I found [his appearance] almost comical. He was then twenty-three years old; he had something quite irregular in his entire form and had a strange coiffure. His hair rose almost six inches above his forehead into a tousled crest that gave him a strange, bewildered look." Another comes from Kierkegaard's niece, Henriette Lund (1829–1909). When Søren Kierkegaard was a little boy he "was of slender and delicate appearance, and ran about in a little coat of red-cabbage color. He used to be called ‘fork’ by his father, because of his tendency, developed quite early, toward satirical remarks. Although a serious, almost austere tone pervaded the Kierkegaard’s house, I have the firm impression that there was a place for youthful vivacity too, even though of a more sedate and home-made kind than one is used to nowadays. The house was open for an 'old-fashioned hospitality'" (1876).

An important aspect of Kierkegaard's life – generally considered to have had a major influence on his work – was his broken engagement to Regine Olsen (1822–1904). Kierkegaard and Olsen met on 8 May 1837 and were instantly attracted to each other, but sometime around 11 August 1838 he had second thoughts. In his journals, Kierkegaard wrote idealistically about his love for her:

He was writing about the inner being in all of these books and his goal was to get the single individual away from all the speculation that was going on about God and Christ. Speculation creates quantities of ways to find God and his Goods but finding faith in Christ and putting the understanding to use stops all speculation because then one begins to actually exist as a Christian or in an ethical/religious way. He was against an individual waiting until certain of God's love and salvation before beginning to try to become a Christian. He defined this as a "special type of religious conflict the Germans call Anfechtung" (contesting or disputing). In Kierkegaard's view the Church should not try to prove Christianity or even defend it. It should help the single individual to make a leap of faith, the faith that God is love and has a task for that very same single individual. He wrote the following about fear and trembling and love as early as 1839, "Fear and trembling is not the primus motor in the Christian life, for it is love; but it is what the oscillating balance wheel is to the clock-it is the oscillating balance wheel of the Christian life.

On 8 September 1840, Kierkegaard formally proposed to Olsen. He soon felt disillusioned about his prospects. He broke off the engagement on 11 August 1841, though it is generally believed that the two were deeply in love. In his journals, Kierkegaard mentions his belief that his "melancholy" made him unsuitable for marriage, but his precise motive for ending the engagement remains unclear.

Kierkegaard published some of his works using pseudonyms and for others he signed his own name as author. Whether being published under pseudonym or not, Kierkegaard's central writings on religion have included Fear and Trembling and Either/Or, the latter of which is considered to be his magnum opus. Pseudonyms were used often in the early 19th century as a means of representing viewpoints other than the author's own; examples include the Writers of the Federalist Papers and the Anti-Federalist Papers. Kierkegaard employed the same technique as a way to provide examples of indirect communication. In writing under various pseudonyms to express sometimes contradictory positions, Kierkegaard is sometimes criticized for playing with various viewpoints without ever committing to one in particular. He has been described by those opposing his writings as indeterminate in his standpoint as a Writer, though he himself has testified to all his work deriving from a Service to Christianity. After On the Concept of Irony with Continual Reference to Socrates, his 1841 doctoral thesis under Frederik Christian Sibbern (da), he wrote his first book under the pseudonym "Johannes Climacus" (after John Climacus) between 1841–1842. De omnibus dubitandum est (Latin: "Everything must be doubted") was not published until after his death.

Faith was something that Kierkegaard often wrestled with throughout his writing career; under both his real name and behind pseudonyms, he explored many different aspects of faith. These various aspects include faith as a spiritual goal, the historical orientation of faith (particularly toward Jesus Christ), faith being a gift from God, faith as dependency on a historical object, faith as a passion, and faith as a resolution to personal despair. Even so, it has been argued that Kierkegaard never offers a full, explicit and systematic account of what faith is. Either/Or was published 20 February 1843; it was mostly written during Kierkegaard's stay in Berlin, where he took notes on Schelling's Philosophy of Revelation. According to the Routledge Companion to Philosophy and Religion, Either/Or (vol. 1) consists of essays of literary and music criticism, a set of romantic-like-aphorisms, a whimsical essay on how to avoid boredom, a panegyric on the unhappiest possible human being, a diary recounting a supposed seduction, and (vol. II) two enormous didactic and hortatory ethical letters and a sermon. This opinion is a reminder of the type of controversy Kierkegaard tried to encourage in many of his writings both for readers in his own generation and for subsequent generations as well.

He also wrote several more pseudonymous books in 1844: Philosophical Fragments, Prefaces and The Concept of Anxiety and finished the year up with Four Upbuilding Discourses, 1844. He used indirect communication in the first book and direct communication in the rest of them. He doesn't believe the question about God's existence should be an opinion held by one group and differently by another no matter how many demonstrations are made. He says it's up to the single individual to make the fruit of the Holy Spirit real because love and joy are always just possibilities. Christendom wanted to define God's attributes once and for all but Kierkegaard was against this. His love for Regine was a disaster but it helped him because of his point of view.

On 22 December 1845, Peder Ludvig Møller, who studied at the University of Copenhagen at the same time as Kierkegaard, published an article indirectly criticizing Stages on Life's Way. The article complimented Kierkegaard for his wit and intellect, but questioned whether he would ever be able to master his talent and write coherent, complete works. Møller was also a contributor to and Editor of The Corsair, a Danish satirical paper that lampooned everyone of notable standing. Kierkegaard published a sarcastic response, charging that Møller's article was merely an attempt to impress Copenhagen's literary elite.

There had been much discussion in Denmark about the pseudonymous authors until the publication of Concluding Unscientific Postscript to Philosophical Fragments, 27 February 1846, where he openly admitted to be the author of the books because people began wondering if he was, in fact, a Christian or not. Several Journal entries from that year shed some light on what Kierkegaard hoped to achieve. This book was published under an earlier pseudonym, Johannes Climacus. On 30 March 1846 he published Two Ages: A Literary Review, under his own name. A critique of the novel Two Ages (in some translations Two Generations) written by Thomasine Christine Gyllembourg-Ehrensvärd, Kierkegaard made several insightful observations on what he considered the nature of modernity and its passionless attitude towards life. Kierkegaard writes that "the present age is essentially a sensible age, devoid of passion ... The trend today is in the direction of mathematical equality, so that in all classes about so and so many uniformly make one individual". In this, Kierkegaard attacked the conformity and assimilation of individuals into "the crowd" which became the standard for truth, since it was the numerical. How can one love the neighbor if the neighbor is always regarded as the wealthy or the poor or the lame?

Kierkegaard described the hope the witness to the truth has in 1847.

Kierkegaard tried to explain his prolific use of pseudonyms again in The Point of View of My Work as an Author, his autobiographical explanation for his writing style. The book was finished in 1848, but not published until after his death by his brother Christian Peter Kierkegaard. Walter Lowrie mentioned Kierkegaard's "profound religious experience of Holy Week 1848" as a turning point from "indirect communication" to "direct communication" regarding Christianity. However, Kierkegaard stated that he was a religious author throughout all of his writings and that his aim was to discuss "the Problem 'of becoming a Christian', with a direct polemic against the monstrous illusion we call Christendom". He expressed the illusion this way in his 1848 "Christian Address", Thoughts Which Wound From Behind – for Edification.

The Second edition of Either/Or was published early in 1849. Later that year he published The Sickness Unto Death, under the pseudonym Anti-Climacus. He's against Johannes Climacus who kept writing books about trying to understand Christianity. Here he says, "Let others admire and praise the person who pretends to comprehend Christianity. I regard it as a plain ethical task – perhaps requiring not a little self-denial in these speculative times, when all 'the others' are busy with comprehending-to admit that one is neither able nor supposed to comprehend it." Sickness unto death was a familiar phrase in Kierkegaard's earlier writings. This sickness is despair and for Kierkegaard despair is a sin. Despair is the impossibility of possibility. Kierkegaard writes:

In September 1850, the Western Literary Messenger wrote: "While Martensen with his wealth of genius casts from his central position light upon every sphere of existence, upon all the phenomena of life, Søren Kierkegaard stands like another Simon Stylites, upon his solitary column, with his eye unchangeably fixed upon one point." In 1855, the Danish National Church published his obituary. Kierkegaard did have an impact there judging from the following quote from their article: "The fatal fruits which Dr. Kierkegaard show to arise from the union of Church and State, have strengthened the scruples of many of the believing laity, who now feel that they can remain no longer in the Church, because thereby they are in communion with unbelievers, for there is no ecclesiastical discipline."

In 1851 Kierkegaard wrote his Two Discourses at the Communion on Fridays where he once more discussed sin, forgiveness, and authority using that same verse from 1 Peter 4:8 that he used twice in 1843 with his Three Upbuilding Discourses, 1843.

He now pointedly referred to the acting single individual in his next three publications; For Self-Examination, Two Discourses at the Communion on Fridays, and in 1852 Judge for Yourselves!. Judge for Yourselves! was published posthumously in 1876.

Changes did occur in the administration of the Church and these changes were linked to Kierkegaard's writings. The Church noted that dissent was "something foreign to the national mind". On 5 April 1855 the Church enacted new policies: "every member of a congregation is free to attend the ministry of any clergyman, and is not, as formerly, bound to the one whose parishioner he is". In March 1857, compulsory infant baptism was abolished. Debates sprang up over the King's position as the head of the Church and over whether to adopt a constitution. Grundtvig objected to having any written rules. Immediately following this announcement the "agitation occasioned by Kierkegaard" was mentioned. Kierkegaard was accused of Weigelianism and Darbyism, but the article continued to say, "One great truth has been made prominent, viz (namely): That there exists a worldly-minded clergy; that many things in the Church are rotten; that all need daily repentance; that one must never be contented with the existing state of either the Church or her Pastors."

Several of Kierkegaard's works were translated into German from 1861 onward, including excerpts from Practice in Christianity (1872), from Fear and Trembling and Concluding Unscientific Postscript (1874), Four Upbuilding Discourses and Christian Discourses (1875), and The Lillis of the Field and the Birds of the Air (1876) according to Kierkegaard's International Reception: Northern and Western Europe: Toma I, by John Stewart, see p. 388ff' The Sickness Unto Death, 1881 Twelve speeches by Søren Kierkegaard, by Julius Fricke, 1886 Stages on Life's Way, 1886 (Bärthold).

"August Strindberg was influenced by the Danish individualistic Philosopher Kierkegaard while a student at Uppsala University (1867–1870) and mentioned him in his book Growth of a Soul as well as Zones of the Spirit (1913). Edwin Bjorkman credited Kierkegaard as well as Henry Thomas Buckle and Eduard von Hartmann with shaping Strindberg's artistic form until he was strong enough to stand wholly on his own feet." The dramatist Henrik Ibsen is said to have become interested in Kierkegaard as well as the Norwegian national Writer and poet Bjørnstjerne Bjørnson (1832–1910) who named one of his characters Søren Pedersen in his 1890 book In God's Way. Kierkegaard's father's name was Michael Pedersen Kierkegaard.

Austrian Psychologist Wilhelm Stekel (1868–1940) referred to Kierkegaard as the "fanatical follower of Don Juan, himself the Philosopher of Don Juanism" in his book Disguises of Love. German Psychiatrist and Philosopher Karl Jaspers (1883–1969) stated he had been reading Kierkegaard since 1914 and compared Kierkegaard's writings with Friedrich Hegel's Phenomenology of Mind and the writings of Friedrich Nietzsche. Jaspers saw Kierkegaard as a champion of Christianity and Nietzsche as a champion for atheism. Later, in 1935, Karl Jaspers emphasized Kierkegaard's (and Nietzsche's) continuing importance for modern philosophy

The first academic to draw attention to Kierkegaard was fellow Dane Georg Brandes, who published in German as well as Danish. Brandes gave the first formal lectures on Kierkegaard in Copenhagen and helped bring him to the attention of the European intellectual community. Brandes published the first book on Kierkegaard's philosophy and life, Søren Kierkegaard, ein literarisches Charakterbild. Autorisirte deutsche Ausg (1879) and compared him to Hegel and Tycho Brahe in Reminiscences of my Childhood and Youth (1906). Brandes also discussed the Corsair Affair in the same book. Brandes opposed Kierkegaard's ideas in the 1911 edition of the Britannica. Brandes compared Kierkegaard to Nietzsche as well. Brandes also mentioned Kierkegaard extensively in volume 2 of his 6 volume work, Main Currents in Nineteenth Century Literature (1872 in German and Danish, 1906 English).

Otto Pfleiderer in The Philosophy of Religion: On the Basis of Its History (1887), claimed that Kierkegaard presented an anti-rational view of Christianity. He went on to assert that the ethical side of a human being has to disappear completely in his one-sided view of faith as the highest good. He wrote, "Kierkegaard can only find true Christianity in entire renunciation of the world, in the following of Christ in lowliness and suffering especially when met by hatred and persecution on the part of the world. Hence his passionate polemic against ecclesiastical Christianity, which he says has fallen away from Christ by coming to a peaceful understanding with the world and conforming itself to the world's life. True Christianity, on the contrary, is constant polemical pathos, a battle against reason, nature, and the world; its commandment is enmity with the world; its way of life is the death of the naturally human."

An article from an 1889 dictionary of religion revealed a good idea of how Kierkegaard was regarded at that time, stating: "Having never left his native city more than a few days at a time, excepting once, when he went to Germany to study Schelling's philosophy. He was the most original thinker and theological Philosopher the North ever produced. His fame has been steadily growing since his death, and he bids fair to become the leading religio-philosophical light of Germany, not only his theological, but also his aesthetic works have of late become the subject of universal study in Europe."

During the 1890s, Japanese Philosophers began disseminating the works of Kierkegaard, from the Danish thinkers. Tetsuro Watsuji was one of the first Philosophers outside of Scandinavia to write an introduction on his philosophy, in 1915.

Harald Høffding wrote an article about him in A brief history of modern philosophy (1900). Høffding mentioned Kierkegaard in Philosophy of Religion 1906, and the American Journal of Theology (1908) printed an article about Hoffding's Philosophy of Religion. Then Høffding repented of his previous convictions in The problems of philosophy (1913). Høffding was also a friend of the American Philosopher william James, and although James had not read Kierkegaard's works, as they were not yet translated into English, he attended the lectures about Kierkegaard by Høffding and agreed with much of those lectures. James' favorite quote from Kierkegaard came from Høffding: "We live forwards but we understand backwards". william James wrote:

Hermann Gottsche published Kierkegaard's Journals in 1905. It had taken academics 50 years to arrange his journals. Kierkegaard's main works were translated into German by Christoph Schrempf from 1909 onwards. Emmanuel Hirsch released a German edition of Kierkegaard's collected works from 1950 onwards. Both Harald Hoffding's and Schrempf's books about Kierkegaard were reviewed in 1892.

The Encyclopaedia of religion and ethics had an article about Kierkegaard in 1908. The article began:

Friedrich von Hügel wrote about Kierkegaard in his 1913 book, Eternal life: a study of its implications and applications, where he said: "Kierkegaard, the deep, melancholy, strenuous, utterly uncompromising Danish religionist, is a spiritual brother of the great Frenchman, Blaise Pascal, and of the striking English Tractarian, Hurrell Froude, who died young and still full of crudity, yet left an abiding mark upon all who knew him well."

John George Robertson wrote an article called Soren Kierkegaard in 1914: "Notwithstanding the fact that during the last quarter of a century, we have devoted considerable attention to the literatures of the North, the thinker and man of letters whose name stands at the head of the present article is but little known to the English-speaking world. The Norwegians, Ibsen and Bjørnson, have exerted a very real power on our intellectual life, and for Bjørnson we have cherished even a kind of affection. But Kierkegaard, the Writer who holds the indispensable key to the intellectual life of Scandinavia, to whom Denmark in particular looks up as her most original man of genius in the nineteenth century, we have wholly overlooked." Robertson wrote previously in Cosmopolis (1898) about Kierkegaard and Nietzsche. Theodor Haecker wrote an essay titled, Kierkegaard and the Philosophy of Inwardness in 1913 and David F. Swenson wrote a biography of Søren Kierkegaard in 1920. Lee M. Hollander translated parts of Either/Or, Fear and Trembling, Stages on Life's Way, and Preparations for the Christian Life (Practice in Christianity) into English in 1923, with little impact. Swenson wrote about Kierkegaard's idea of "armed neutrality" in 1918 and a lengthy article about Søren Kierkegaard in 1920. Swenson stated: "It would be interesting to speculate upon the reputation that Kierkegaard might have attained, and the extent of the influence he might have exerted, if he had written in one of the major European languages, instead of in the tongue of one of the smallest countries in the world."

Kierkegaard's comparatively early and manifold philosophical and theological reception in Germany was one of the decisive factors of expanding his works' influence and readership throughout the world. Important for the first phase of his reception in Germany was the establishment of the journal Zwischen den Zeiten (Between the Ages) in 1922 by a heterogeneous circle of Protestant theologians: Karl Barth, Emil Brunner, Rudolf Bultmann and Friedrich Gogarten. Their thought would soon be referred to as dialectical theology. At roughly the same time, Kierkegaard was discovered by several proponents of the Jewish-Christian philosophy of dialogue in Germany, namely by Martin Buber, Ferdinand Ebner, and Franz Rosenzweig. In addition to the philosophy of dialogue, existential philosophy has its point of origin in Kierkegaard and his concept of individuality. Martin Heidegger sparsely refers to Kierkegaard in Being and Time (1927), obscuring how much he owes to him. Walter Kaufmann discussed Sartre, Jaspers, and Heidegger in relation to Kierkegaard, and Kierkegaard in relation to the crisis of religion in the 1960s. Later, Kierkegaard's Fear and Trembling (Series Two) and The Sickness Unto Death (Series Three) were included in the Penguin Great Ideas Series (Two and Three).

Philosophers and Theologians influenced by Kierkegaard are numerous and include major twentieth century Theologians and Philosophers. Paul Feyerabend's epistemological anarchism in the philosophy of science was inspired by Kierkegaard's idea of subjectivity as truth. Ludwig Wittgenstein was immensely influenced and humbled by Kierkegaard, claiming that "Kierkegaard is far too deep for me, anyhow. He bewilders me without working the good effects which he would in deeper souls". Karl Popper referred to Kierkegaard as "the great reformer of Christian ethics, who exposed the official Christian morality of his day as anti-Christian and anti-humanitarian hypocrisy". Hilary Putnam admires Kierkegaard, "for his insistence on the priority of the question, 'How should I live?'". By the early 1930s, Jacques Ellul's three primary sources of inspiration were Karl Marx, Søren Kierkegaard, and Karl Barth. According to Ellul, Marx and Kierkegaard were his two greatest influences, and the only two authors of which he read all of their work.

Wilhelm Pauk wrote in 1931 (Karl Barth Prophet Of A New Christianity) that Kierkegaard's use of the Latin phrase Finitum Non Capax Infiniti (the finite does not (or cannot) comprehend the infinite) summed up Barth's system. David G. Kingman and Adolph Keller each discussed Barth's relationship to Kierkegaard in their books, The Religious Educational Values in Karl Barth's Teachings (1934) and Karl Barth and Christian Unity (1933). Keller notes the splits that happen when a new teaching is introduced and some assume a higher knowledge from a higher source than others. But Kierkegaard always referred to the equality of all in the world of the spirit where there is neither "sport" nor "spook" or anyone who can shut you out of the world of the spirit except yourself. All are chosen by God and equal in His sight. The Expectancy of Faith," Before this faith came, we were held prisoners by the law, locked up until faith should be revealed. So the law was put in charge to lead us to Christ that we might be justified by faith. Now that faith has come, we are no longer under the supervision of the law. You are all sons of God through faith in Christ Jesus, for all of you who were baptized into Christ have clothed yourselves with Christ. There is neither Jew nor Greek, slave nor free, male nor female, for you are all one in Christ Jesus. If you belong to Christ, then you are Abraham's seed, and heirs according to the promise. The Bible – NIV" Galatians 3:23–29; "In the world of spirit to become one’s own master, is the highest – and in love to help someone toward that, to become himself, free, independent, his own master, to help him stand alone – that is the greatest beneficence. The greatest beneficence, to help the other to stand alone, cannot be done directly." "If a person always keeps his soul sober and alert in this idea, he will never go astray in his outlook on life and people or "combine respect for status of persons with his faith." Show no partiality as you hold the faith of our Lord Jesus Christ. (James 2.1) Then he will direct his thoughts toward God, and his eye will not make the mistake of looking for differences in the world instead of likeness with God.

According to Samuel Hugo Bergmann, "Kierkegaard's journals are one of the most important sources for an understanding of his philosophy". Kierkegaard wrote over 7,000 pages in his journals on events, musings, thoughts about his works and everyday remarks. The entire collection of Danish journals (Journalen) was edited and published in 13 volumes consisting of 25 separate bindings including indices. The first English edition of the journals was edited by Alexander Dru in 1938. The style is "literary and poetic [in] manner".

Nikolai Berdyaev makes a related argument against reason in his 1945 book The Divine and the Human.

William Hubben compared Kierkegaard to Dostoevsky in his 1952 book Four Prophets of Our Destiny, later titled Dostoevsky, Kierkegaard, Nietzsche, and Kafka.

In 1955 Morton White wrote about the word "exists" and Kierkegaard's idea of God's is-ness.

Kierkegaardian scholar Paul Holmer described Kierkegaard's wish in his introduction to the 1958 publication of Kierkegaard's Edifying Discourses where he wrote:

John Daniel Wild noted as early as 1959 that Kierkegaard's works had been "translated into almost every important living language including Chinese, Japanese, and Korean, and it is now fair to say that his ideas are almost as widely known and as influential in the world as those of his great opponent Hegel, still the most potent of world Philosophers."

Mortimer J. Adler wrote the following about Kierkegaard in 1962:

Kierkegaard has also had a considerable influence on 20th-century literature. Figures deeply influenced by his work include W. H. Auden, Jorge Luis Borges, Don DeLillo, Hermann Hesse, Franz Kafka, David Lodge, Flannery O'Connor, Walker Percy, Rainer Maria Rilke, J.D. Salinger and John Updike. What George Henry Price wrote in his 1963 book The Narrow Pass regarding the "who" and the "what" of Kierkegaard still seems to hold true today: "Kierkegaard was the sanest man of his generation....Kierkegaard was a schizophrenic....Kierkegaard was the greatest Dane....the difficult Dane....the gloomy Dane...Kierkegaard was the greatest Christian of the century....Kierkegaard's aim was the destruction of the historic Christian faith....He did not attack philosophy as such....He negated reason....He was a voluntarist....Kierkegaard was the Knight of Faith....Kierkegaard never found faith....Kierkegaard possessed the truth....Kierkegaard was one of the damned."

In 1964 Life Magazine traced the history of existentialism from Heraclitus (500BC) and Parmenides over the argument over The Unchanging One as the real and the state of flux as the real. From there to the Old Testament Psalms and then to Jesus and later from Jacob Boehme (1575–1624) to Rene Descartes (1596–1650) and Blaise Pascal (1623–1662) and then on to Nietzsche and Paul Tillich. Dostoevski and Camus are attempts to rewrite Descartes according to their own Lights and Descartes is the forefather of Sartre through the fact that they both used a "literary style." The article goes on to say,

Kierkegaard had a profound influence on psychology. He is widely regarded as the founder of Christian psychology and of existential psychology and therapy. Existentialist (often called "humanistic") Psychologists and therapists include Ludwig Binswanger, Viktor Frankl, Erich Fromm, Carl Rogers, and Rollo May. May based his The Meaning of Anxiety on Kierkegaard's The Concept of Anxiety. Kierkegaard's sociological work Two Ages: The Age of Revolution and the Present Age critiques modernity. Ernest Becker based his 1974 Pulitzer Prize book, The Denial of Death, on the writings of Kierkegaard, Freud and Otto Rank. Kierkegaard is also seen as an important precursor of postmodernism. Danish priest Johannes Møllehave has lectured about Kierkegaard. In popular culture, he was the subject of serious television and radio programmes; in 1984, a six-part documentary Sea of Faith: Television series presented by Don Cupitt featured an episode on Kierkegaard, while on Maundy Thursday in 2008, Kierkegaard was the subject of discussion of the BBC Radio 4 programme presented by Melvyn Bragg, In Our Time, during which it was suggested that Kierkegaard straddles the analytic/continental divide. Google honoured him with a Google Doodle on his 200th anniversary.

Kierkegaard came to hope that no one would retain their sins even though they have been forgiven. And by the same token that no one who truly believed in the forgiveness of sin would live their own life as an objection against the existence of forgiveness. He made the point that Cato committed suicide before Caesar had a chance to forgive him. This fear of not finding forgiveness is devastating. Edna H. Hong quoted Kierkegaard in her 1984 book, Forgiveness is a Work As Well As a Grace and Kierkegaard wrote about forgiveness in 1847. In 1954, Samuel Barber set to music Kierkegaard's prayer, "Father in Heaven! Hold not our sins up against us but hold us up against our sins so that the thought of You when it wakens in our soul, and each time it wakens, should not remind us of what we have committed but of what You did forgive, not of how we went astray but of how You did save us!"

Kierkegaard also stresses the importance of the self, and the self's relation to the world, as being grounded in self-reflection and introspection. He argued in Concluding Unscientific Postscript to Philosophical Fragments that "subjectivity is truth" and "truth is subjectivity." This has to do with a distinction between what is objectively true and an individual's subjective relation (such as indifference or commitment) to that truth. People who in some sense believe the same things may relate to those beliefs quite differently. Two individuals may both believe that many of those around them are poor and deserve help, but this knowledge may lead only one of them to decide to actually help the poor. This is how Kierkegaard put it: "What a priceless invention statistics are, what a glorious fruit of culture, what a characteristic counterpart to the de te narratur fabula [the tale is told about you] of antiquity. Schleiermacher so enthusiastically declares that knowledge does not perturb religiousness, and that the religious person does not sit safeguarded by a lightning rod and scoff at God; yet with the help of statistical tables one laughs at all of life." In other words, Kierkegaard says: "Who has the more difficult task: the Teacher who lectures on earnest things a meteor's distance from everyday life – or the learner who should put it to use?" This is how it was summed up in 1940.

Kierkegaard first moved to action after Professor (soon bishop) Hans Lassen Martensen gave a speech in church in which he called the recently deceased Bishop Jacob Peter Mynster a "truth-witness, one of the authentic truth-witnesses". Kierkegaard explained, in his first article, that Mynster's death permitted him—at last—to be frank about his opinions. He later wrote that all his former output had been "preparations" for this attack, postponed for years waiting for two preconditions: 1) both his father and bishop Mynster should be dead before the attack and 2) he should himself have acquired a name as a famous theologic Writer. Kierkegaard's father had been Mynster's close friend, but Søren had long come to see that Mynster's conception of Christianity was mistaken, demanding too little of its adherents. Kierkegaard strongly objected to the portrayal of Mynster as a 'truth-witness'.

Kierkegaard’s influence on Karl Barth’s early theology is evident in The Epistle to the Romans. The early Barth read at least three volumes of Kierkegaard’s works: Practice in Christianity, The Moment, and an Anthology from his journals and diaries. Almost all key terms from Kierkegaard which had an important role in The Epistle to the Romans can be found in Practice in Christianity. The concept of the indirect communication, the paradox, and the moment of Practice in Christianity, in particular, confirmed and sharpened Barth’s ideas on contemporary Christianity and the Christian life.