Missing from this post is The Sickness Unto Death, which I think is the most important of anything he wrote. The book is about what a Christian ought to think of what it means to live and what it means to die.

> What if grace doesn’t come as a gift bestowed from beyond, but in moments of self-forgetfulness, moments in which, by whatever means and processes, the Ego simply disappears? Questions about the afterlife are not answered in this kind of thinking, but so what? If one isn’t afraid to live, why should one be afraid to die? And even if one is afraid, again, so what? Our courage and our fear will not change the fact of our dying.

https://www.naturalthinker.net/trl/texts/Kierkegaard,Soren/T...

> Oh, but even if Christ had not awakened Lazarus from the dead, is it not true that this sickness, that death itself, was not a sickness unto death? When Christ comes to the grave and cries with a loud voice, "Lazarus, come forth" (11:43), it is evident enough that "this" sickness is not unto death. But even if Christ had not said these words -- merely the fact that He, who is "the resurrection and the life" (11:25), comes to the grave, is not this a sufficient sign that this sickness is not unto death, does not the fact that Christ exists mean that this sickness is not unto death? And what help would it have been to Lazarus to be awakened from the dead, if the thing must end after all with his dying -- how would that have helped Lazarus, if He did not live who is the resurrection and the life for everyone who believes in Him? No, it is not because Lazarus was awakened from the dead, not for this can one say that this sickness is not unto death; but because He lives, therefore this sickness is not unto death. For, humanly speaking, death is the last thing of all; and, humanly speaking, there is hope only so long as there is life. But Christianly understood death is by no means the last thing of all, hence it is only a little event within that which is all, an eternal life; and Christianly understood there is in death infinitely much more hope than merely humanly speaking there is when there not only is life but this life exhibits the fullest health and vigor.

edit: Not removing the original wording, but it's an overstatement to say that Sickness Unto Death could be regarded as Kierkegaard's most important work. It's definitely not. It's just his writing that is most relevant to what the author of this post is talking about.