Goodness in the natural order vs its corruption
I just read this comment on the parasitic and derivative nature of evil. I think it is well-phrased and insightful.
Evil doesn't exist as a created thing, in the way a tree does. It is defined by what it is not. Darkness doesn't exist either; it's a lack of light. There are no darkness particles or darkness waves.
In the same way, evil is a lack of goodness. Rape could not exist without sex, but sex could exist without rape. There cannot be murder without the existence of life, but life could exist without murder. A lie could not happen without the existence of truth, but the truth could exist without lies.
This is how we know two other things. God is good, because all things in existence are good. Good (and thus God) is also infinitely greater and more powerful than evil, since evil can't even exist on its own.