Christianity does not claim to have the answer to this question. It starts from the position that there is inexcusable evil in the world, ultimately unjustified by any cosmic system. Rather we ask, given that evil, what can we do? Christ has given an answer, to identify with those suffering from that evil and kill a measure of that evil in our own deaths and thus open a door to something more. In fact Christ's death rejects theodicy in the sense that it rejects a justification for evil and death and demands vindication.
"I seriously doubt that, sir, but this is America and I would die for your right to make outrageous claims." - Bill McNeal