Kierkegaard on Constructing the Self

In order to understand the following quote from philosopher Søren Kierkegaard, a bit of background on terminology is required. This passage comes from a book about despair, which, for Kierkegaard, arises out of a wrong relation of the self to itself and also to God, the eternal. The self—my self, myself—is a synthesis or unity of two elements: first, necessity or concreteness (also, finitude), which refers to the given elements that make up who I am (e.g., personality, attitudes, talents, location); and second, possibility or abstraction, which refers to the openness to forging in some new direction, taking up some new possibility, transcending the current circumstance. Hopefully that will help a bit with the following brilliant passage on self-construction:

In order to want in despair to be oneself [one form of despair], there must be consciousness of an infinite self. However, this infinite self is really only the most abstract form of the self, the most abstract possibility of the self. And it is this self the despairer wants to be, severing the self from any relation to the power which has established it [that is, God], or severing it from the conception that there is such a power. By means of this infinite form, the self wants in despair to rule over himself, or create himself, make this self the self he wants to be, determine what he will have and what he will not have in his concrete self. His concrete self, or his concreteness, has indeed necessity and limits, is this quite definite thing, with these aptitudes, predispositions, etc., in this concrete set of circumstances, etc. But by means of the infinite form, the negative self, he wants first to undertake to refashion the whole thing, in order to get out of it a self such as he wants, produced by means of the infinite form of the negative self—and it is in this way he wants to be himself. That is to say, he wants to begin a little earlier than other people, not at and with the beginning, but “in the beginning”; he does not want to don his own self, does not want to see his task in his given self, he wants, by virtue of being the infinite form, to construct it himself. (The Sickness Unto Death, 82-3.)

I wonder what, taking this text as a key, a Kierkegaardian analysis of atheistic existentialism (à la Sartre, for example) would look like.