The Concept of Anxiety
All of Kierkegaard's books have either a preface, dedication, or prayer at the beginning. This book includes a lengthy introduction. "The Concept of Anxiety" was published on exactly the same date as "Prefaces", June 17, 1844. Both books deal with Hegel’s idea of mediation. Mediation is a common thread throughout Kierkegaard’s works. His work up to this point was to show that faith was being mediated by knowledge. Here he takes up the questions of sin and guilt.
Either/Or
Kierkegaard later referred to his concept of choosing yourself as the single individual in "The Concept of Anxiety", June 17, 1844, and then in his "", August 31, 1844, and once again in "Upbuilding Discourses in Various Spirits", 1847. William James echoed Kierkegaard in his lecture on "The Sick Soul" where he wrote, "the man must die to an unreal life before he can be born into the real life." You are outside yourself and therefore cannot do without the other as opposition; you believe that only a restless spirit is alive, and all who are experienced believe that only a quiet spirit is truly alive. For you a turbulent sea is a symbol of life; for me it is the quiet, deep water. "Either/Or Part II" p. 144, HongAnxiety is a qualification of dreaming spirit, and as such it has its place in psychology. Awake, the difference between myself and my other is posited; sleeping, it is suspended; dreaming, it is an intimated nothing. The actuality of the spirit constantly shows itself as a form that tempts its possibility but disappears as soon as it seeks to grasp for it, and it is a nothing that can only bring anxiety. More it cannot do as long as it merely shows itself. The concept of anxiety is almost never treated in psychology. Therefore, I must point out that it is altogether different from fear and similar concepts that refer to something definite, whereas anxiety is freedom’s actuality as the possibility of possibility. For this reason, anxiety is not found in the beast, precisely because by nature the beast is not qualified as spirit. "The Concept of Anxiety", Nichol p. 42 
Now he discovers that the self he chooses has a boundless multiplicity within itself inasmuch as it has a history, a history in which he acknowledges identity with himself. This history is of a different kind, for in this history he stands in relation to other individuals in the race, and to the whole race, and this history contains painful things, and yet he is the person he is only through this history. That is why it takes courage to choose oneself, for at the same time as he seems to be isolating himself most radically he is most radically sinking himself into the root by which he is bound up with the whole. This makes him uneasy, and yet it must be so, for when the passion of freedom is aroused in him-and it is aroused in the choice just as it presupposes itself in the choice-he chooses himself and struggles for this possession as for his salvation, and it is his salvation. "Either/Or Part II", Hong, p. 216When a person turns and faces himself in order to understand himself, he steps, as it were, in the way of that first self, halts that which was turned outward in hankering for and seeking after the surrounding world that is its object, and summons it back from the external. In order to prompt the first self to this withdrawal, the deeper self lets the surrounding world remain what it is-remain dubious. This is indeed the way it is; the world around us is inconstant and can be changed into the opposite at any moment, and there is not one person who can force this change by his own might or by the conjuration of his wish. The deeper self now shapes the deceitful flexibility of the surrounding world in such a way that it is no longer attractive to the first self. Then the first self either must proceed to kill the deeper self, to render it forgotten, whereby the whole matter is given up; or it must admit that the deeper self is right, because to want to predicate constancy of something that continually changes is indeed a contradiction, and as soon as one confesses that it changes, it can of course, change in that same moment. However much that first self shrinks from this, there is no wordsmith so ingenious or no thought-twister so wily that he can invalidate the deeper self’s eternal claim. There is only one way out, and that is to silence the deeper self by letting the roar of inconstancy drown it out. "Eighteen Upbuilding Discourses", 1845, Hong translation, p. 314Just as a man changes his clothes for celebration, so a person preparing for the holy act of confession is inwardly changed. It is indeed like changing one’s clothes to divest oneself of multiplicity in order to make up one’s mind about one thing, to interrupt the pace of busy activity in order to put on the repose of contemplation in unity with oneself. And this unity with oneself is the celebration’s simple festive dress that is the condition of admittance. "Upbuilding Discourses in Various Spirits", Søren Kierkegaard, 1847, Hong, p. 19If a person whose life has been tried in some crucial difficulty has a friend and sometime later he is unable to retain the past clearly, if anxiety creates confusion, and if accusing thoughts assail him with all their might as he works his way back, then he may go to his friend and say, "My soul is sick so that nothing will become clear to me, but I confided everything to you; you remember it, so please explain the past to me again." But if a person has no friend, he presumably goes to God if under other circumstances he has confided something to him, if in the hour of decision he called God as witness when no one understood him. And the one who went to his friend perhaps was not understood at times, perhaps was filled with self-loathing, which is even more oppressive, upon discovering that the one to whom he had confided his troubles had not understood him at all, even though he had listened, had not sensed what was making him anxious, but had only an inquisitive interest in his unusual encounter with life. But this would never happen with God; who would dare to venture to think this of God, even if he is cowardly enough to prefer to forget God-until he stands face-to-face with the judge, who passes judgment on him but not on the one who truly has God as a witness, because where God is the judge, there is indeed no judge if God is the witness. It by no means follows that a person’s life becomes easy because he learns to know God in this way. On the contrary, it can become very hard; it may become more difficult than the contemptible easiness of sensate human life, but in this difficulty life also acquires ever deeper and deeper meaning. Søren Kierkegaard, "Four Upbuilding Discourses" August 31, 1844 ("Eighteen Upbuilding Discourses" p. 324)
August Strindberg was familiar with "Either/Or" and this book made him "forever a champion of the ethical as juxtaposed to the aesthetic life conception and he always remained faithful to the idea that art and knowledge must be subservient to life, and that life itself must be lived as we know best, chiefly because we are part of it and cannot escape from its promptings." Strindberg was obviously attracted to "Either/Or Part II" where Kierkegaard developed his categorical imperative. He wrote the following in "Growth of a Soul" published posthumously in 1913 about Kierkegaard's "Either—Or": "it was valid only for the priests who called themselves Christians and the seducer and "Don Juan" were the author himself, who satisfied his desires in imagination". Part II was his "Discourse on Life as a Duty, and when he reached the end of the work he found the moral philosopher in despair, and that all this teaching about duty had only produced a Philistine." He then states that Kierkegaard's discourses might have led him closer to Christianity but he didn't know if he could come back to something "which had been torn out, and joyfully thrown into the fire". However, after reading the book he "felt sinful". Then another writer began to influence his life. This is how he described "Either/Or":