Theodicy means vindication of God. It is to answer the question of why a good God permits the manifestation of evil, thus resolving the issue of the problem of evil. wiki
Just as, in my view, the existence of God is often merely defined and deduced into existence, if we accept for the sake of argument that a God, the God, my God does in fact exist, how is the "vindication" of this God in the face of evil not also just defined and deduced into existence?
The point below [and my reaction to it] is taken from my own "on discussing god and religion" thread:
What’s New in….Philosophy of Religion
Daniel Hill describes how the work of Alvin Plantinga has revolutionised Philosophy of Religion.
One argument [against the existence of God] which has shown no sign of diminishing in popularity, still less vanishing, is the problem of evil. This may be expressed very roughly as follows. The set of propositions (1)-(4) is inconsistent, so at least one of them must be wrong:
(1) God is good, and therefore wants to remove evil
(2) God is omniscient, and therefore knows that there is evil
(3) God is omnipotent, and therefore can remove evil
(4) Evil exists.
Now you're talking. This matter is by far -- by far -- the most important question of all in regard to any God and any religion.
Indeed, imagine that we lived in a world where there was no human suffering. A world where no one ever spoke of evil because there was nothing that could be thought of that would allow us to make sense of what some say that it was. Now, in this world, we may well still be unable to demonstrate that an actual God did in fact exist. But when people spoke of Him as loving, just and merciful that would certainly make a whole lot of sense. We may not be able to communicate with or interact with this God, but how could anyone doubt that something "up there" must be sustaining a world totally without pain and suffering.
Let's run this by the religionists here. But, really, how could they not all be reduced down to this: God works in mysterious ways.
Or, for the Buddhists, the universe works in mysterious ways.
But, fortunately enough, for both, one of them results in immortality and the other in salvation. And all the evil in the world doesn't make that go away.