For the invisible things of him from the creation of the world are clearly seen,
being understood by the things that are made,
even his eternal power and Godhead;
so that they are without excuse:
Romans 1:20
"Evil exists because the created universe is not God, but His creation, so it must of necessity fall short of God, who is perfectly Good. After all, if the universe were perfectly good, without evil, it would just be God.
If the universe is God’s creation, then it must fall short of perfection, and it must contain evil, understood as the deprivation of good.
Theism posits a perfect God, and a creation necessarily short of perfection. Theism seems to have gotten this “prediction” quite right, because the cosmos is certainly short of perfection. Theism predicts evil in the world, precisely because God is Good and because the world is not God.
Theism also predicts that we cannot completely understand evil. While some kinds of evil may be understood as the consequence of humans endowed with free will, other kinds of evil are much more difficult to explain in light of an omniscient and omnibenevolent God. Why are there earthquakes and plagues and terrible accidents? Yet theism predicts the need for theodicy. As God is perfect and infinite, we are imperfect and finite, so we cannot expect to understand God’s ways.
But the most striking prediction of theism is that we will recognize evil as evil. That is, theism posits an objective Source of Moral Law and of Goodness against which the cosmos can be measured. If there is no God, there is no objective Source for a distinction between good and evil. If there is no God, there is no overarching “Ought” in the cosmos. There are merely the opinions of men."
EN&V