The FT has a good piece from Martin Amis pondering the mystery of the Holocaust. As Amis notes, history has recorded in painstaking detail the how of the Holocaust, but the why is still a mystery.
Amis, after looking for the answer, ends up agreeing with Primo Levi:
Perhaps one cannot, what is more one must not, understand what happened, because to understand is almost to justify. Let me explain: ‘understanding’ a proposal or human behaviour means to ‘contain’ it, contain its author, put oneself in his place, identify with him. Now, no normal human being will ever be able to identify with Hitler, Himmler, Goebbels, Eichmann, and endless others. This dismays us, and at the same time gives us a sense of relief, because perhaps it is desirable that their words (and also, unfortunately, their deeds) cannot be comprehensible to us. They are non-human words and deeds, really counter-human … [T]here is no rationality in the Nazi hatred; it is a hate that is not in us; it is outside man …
This is of course coterminous with religious questions regarding the Problem of Evil. Putting aside for a moment my reservations on broaching the subject, contemplating other worldviews’ attempt to grapple with the Problem makes one realize how much better Christianity’s “solution” is than any other alternative, unsatisfying though it may be.
Because any attempt to “explain” evil must, in the end, refuse to call evil evil. If evil is explainable, if it is found necessary to sustain some cosmic balance (say), then it is no longer evil. It is drained of scandal, of horror. And if your cosmic scheme provides a coherent explanation for evil, then “God” (or whatever stands for “God”, the cornerstone of your metaphysical system), can no longer be said to be the absolute Good.
Christianity must refrain from furnishing an explanation for evil, or at least a complete one, so that it may be able to, in the words of David Bentley Hart, “hate it with a perfect hatred.” Christianity calls evil evil, with no reservations, no half-measures, no compunction, no buts and, therefore, cannot explain it.
All it can do is point to the Cross.