Philosophy and religion were at odds since Descartes wrote his Principles of Philosophy which called for doubting everything. Soren Kierkegaard questioned this axiom in his book Fear and Trembling as did his pseudonymous author Johannes Climacus.

When the question about truth is asked objectively, truth is reflected upon objectively as an object to which the knower relates himself. What is reflected upon is not the relation but that what he relates himself to is the truth, is true. If only that to which he relates himself is the truth, the true, then the subject is in the truth. When the question about truth is asked subjectively, the individual’s relation is reflected upon subjectively. If only the how of this relation is in truth, the individual is in truth, even if he in this way were to relate himself to untruth. Let us take the knowledge of God as an example. Objectively, what is related upon is that this is the true God; subjectively, that the individual relates himself to a something in such a way that his relation is in truth a God-relation. The existing person who chooses the objective way now enters upon all approximating deliberation intended to bring forth God objectively, which is not achieved in all eternity, because God is a subject and hence only for subjectivity in inwardness. The existing person who chooses the subjective way instantly comprehends the dialectical difficulty because he must use some time, perhaps a long time, to find God objectively. He comprehends this dialectical difficulty in all its pain, because every moment in which he does not have God is wasted. Soren Kierkegaard, (Johannes Climacus) Concluding Unscientific Postscript 1846, Hong p. 199-200

Here is a list of books that lead up to Kierkegaard’s time for your examination.

Not merely in the realm of commerce but in the world of ideas as well our age is organizing a regular clearance sale. Everything is to be had at such a bargain that it is questionable whether in the end there is anybody who will want to bid. Every speculative price-fixer who conscientiously directs attention to the significant march of modern philosophy, every Privatdocent, tutor, and student, every crofter and cottar in philosophy, is not content with doubting everything but goes further. Perhaps it would be untimely and ill-timed to ask them where they are going, but surely it is courteous and unobtrusive to regard it as certain that they have doubted everything, since otherwise it would be a queer thing for them to be going further. This preliminary movement they have therefore all of them made, and presumably with such ease that they do not find it necessary to let drop a word about the how; for not even he who anxiously and with deep concern sought a little enlightenment was able to find any such thing, any guiding sign, any little dietetic prescription, as to how one was to comport oneself in supporting this prodigious task. “But Descartes did it.” Descartes, a venerable, humble and honest thinker, whose writings surely no one can read without the deepest emotion, did what he said and said what he did. Alas, alack, that is a great rarity in our times! Descartes, as he repeatedly affirmed, did not doubt in matters of faith. He did not cry, “Fire!” nor did he make it a duty for everyone to doubt; for Descartes was a quiet and solitary thinker, not a bellowing night-watchman; he modestly admitted that his method had importance for him alone and was justified in part by the bungled knowledge of his earlier years. Soren Kierkegaard, (Johannes Silentio) Fear and Trembling 1843 Preface, tr. Walter Lowrie 1941

Rousseau becomes tutor to young Emile. His method of teaching was unique in many ways and his questions are still important today.

Witty minds have not failed to remark, on the derision expressed by nature, in that she appoints, on this earth, the cattle in the field to be more learned than we, and the bird in the heavens more wise. But has it not been her intention that man should owe his prerogatives to the social affections; should early accustom himself to reciprocal dependence; seeing betimes the impossibility of dispensing with others? Wherefore has she sought to compensate death, not by a cold mechanism, but by the soft and ardent inclination of love? Wherefore has her Author provided by laws, that marriage should spread, and that families, by ingrafting with families, should form new bonds of friendship? Wherefore are his goods so differently appointed to the earth and its dwellers, but to render them social? The fellowship and inequality of men are also nowise among the projects of our wit. They are no inventions of policy, but designs of Providence, which, like all other laws of nature, man has partly misunderstood, and partly abused.
From The Merchant by Hamann

If I wanted to be Lessing’s follower by hook or by crook, I could not; he has prevented it. Just as he himself is free, so, I think, he wants to make everyone free in relation to him, declining the exhalations and impudence of the apprentice, fearful of being made a laughingstock by the tutors: a parroting echo’s routine reproduction of what has been said. 
Soren Kierkegaard Concluding Unscientific Postscript 1846, 1992 P. 72

Has he accepted Christianity, has he rejected it, has he defended it, has he attacked it? 65 With regard to the religious, he always kept something to himself, something that he certainly did say but in a crafty way, something that could not be reeled of by tutors, something that continually remained the same while it continually changed form, something that was not distributed stereotyped for entry in a systematic formula book, but something that a gymnastic dialectician produces and alters and produces, the same and yet not the same. It was downright odious of Lessing continually to change the lettering in connection with the dialectical, just the way a mathematician does and thereby confuses a learner who does not keep his eye mathematically on the demonstration but is satisfied with a fleeting acquaintance that goes by the letter. It was shameful for Lessing to embarrass those who were so exceedingly willing to swear to the master’s words, so that with him they were never able to enter the only relation natural to them: the oath-taking relation. It was shameful of him not to state directly, “I am attacking Christianity,” so that the swearers could say, “We swear.” It was shameful of him not to state directly, “I will defend Christianity,” so that the swears could say, “We swear.”
Soren Kierkegaard enjoyed the writings of Lessing. Kierkegaard wrote about him in his Concluding Unscientific Postscript (1846) tr Hong p. 68 

Lessing closed himself off in the isolation of subjectivity, he did now allow himself to be tricked into becoming world-historical or systematic with regard to the religious, but he understood, and knew how to maintain, that the religious pertained to Lessing and Lessing alone, just as it pertains to every human being in the same way, understood that he had infinitely to do with God, but nothing, nothing to do directly with any human being. p. 65 Lessing has said that contingent historical truths can never become a demonstrations of eternal truths of reason, also that the transition whereby one will build an eternal truth on historical reports is a leap. I shall now scrutinize these two assertions in some detail and correlate them with the issue of Fragments: Can an eternal happiness be build on historical knowledge?
Soren Kierkegaard enjoyed the writings of Lessing. Kierkegaard wrote about him in his Concluding Unscientific Postscript (1846) tr Hong p. 93

The question of the means by which Freedom develops itself to a World, conducts us to the phenomenon of History itself. … Even regarding History as the slaughter-bench at which the happiness of peoples, the wisdom of States, and the virtue of individuals have been victimised — the question involuntarily arises — to what principle, to what final aim these enormous sacrifices have been offered. Hegel’s Philosophy of History III. Philosophic History Sec. 24

In the course of this experience it becomes evident to self-consciousness that life is as essential to it as is sheer self-consciousness. In immediate self-consciousness the simple I is an object that is absolute, albeit one that in itself, as is evident to us, is absolutely mediative, and has the sustainment of its independence as an essential moment. Self-consciousness’s initial experience results in the dissolution of this simple unity; this sets the stage for the emergence of a pure self-consciousness and also a consciousness that doesn’t exist purely for itself but rather for one other than it, the latter being matter-of-factly existent in the manner of a thing. Both moments are essential, although, starting out as unequal and antagonistic, their reflection into unity having not yet taken place, they embody conscious existence in contrary ways: the one is independent, existence-for-self being to it essential; the other is dependent, existing in relation to an other that’s essential to it. The former is master, the latter slave. Hegel’s Phenomenology of Spirit 1807 IV.A. Self-Consciousness Dependent and Independent: Mastery and Servitude Sec. 36

If a German philosopher follows his inclination to put on an act and first transforms himself into a superrational something, just as alchemists and sorcerers bedizen themselves fantastically, in order to answer the question about truth in an extremely satisfying way, this is of no more concern to me than his satisfying answer, which no doubt is extremely satisfying-if one is fantastically dressed up. But whether a German philosopher is or is not doing this can easily be ascertained by anyone who with enthusiasm concentrates his soul on willing to allow himself to be guided by a sage of that kind, and uncritically just uses his guidance compliantly by willing to form his existence according to it. Concluding Unscientific Postscript to Philosophical Fragments by Soren Kierkegaard, 1846, Hong 1992 p. 191

“For all his philosophical and literary interests, Kierkegaard was at heart a preacher, or better still, in the true sense of the word an evangelist, although he always insisted that he wrote as one ‘without authority’.” Key thinkers in Christianity, Edited by Adrian Hastings Alister Mason & Hugh Pyper, 2003.