I’ve always thought that if you couldn’t answer a question simply and shortly, you really didn’t have a good answer. I believe this to be the case with theology as much as anything else. So, to get to the point, here is my tentative answer to the problem of evil:
If evil did not exist, how could the universe overcome it?
A universe with some evil in it and in which that evil is overcome may be better than one in which there was no evil at all and one in which there was evil but in which it was never overcome. A universe with evil is MORE FREE than one which doesn’t have evil, in the sense that it has the ability to do acts an evil-less universe would not.
I’ve never argued God created evil. Evil is an immoral act. God cannot be immoral, hence, he cannot do evil.
I have argued that God either causes pain or permits it. In either case, he wills its existence, and this for a higher good. I do not believe it is just “one” higher good. Rather, many different goods exist because pain exists and therefore justifies, in my opinion, its existence. Some are:
a) The opportunity to be free enough to make certain choices which would be impossible unless pain were present
b) The contrastive good that is afforded by being delivered from pain which would otherwise be impossible to experience
c) The understanding/knowledge that is gained by either suffering for another out of love, or having another suffer for you out of love - such a knowledge and expression of love would not be possible unless pain existed.
I do not claim that ALL good must need involve pain somehow. There are certainly choices that do not require pain to be enjoyed, and goods which do not require contrast to be enjoyed, and knowledge of love that does not require pain to be understood/appreciate. Nevertheless, the goods outlined above are possible goods that would not be present in the universe if pain did not exist.
Indeed, I am not even saying that evil must “necessarily” exist. I’m not sure it is coherent to say that anything in God’s creation “must” exist - as if I must exist or this planet. Things dependent on God’s will, if he is free, do not necessarily exist. It’s sort of like saying “why didn’t God create x universe instead of y?” Well what does it matter, so long as what he made is as good as it can be? Aquinas thought that God could always make better than he did make - for every world he made, he could make another better one - but what he did in fact make, he made as perfect as he could. Perhaps it is then incoherent to talk about things being “necessary” or not. What I am saying is that perhaps the above goods are such that JUSTIFY God’s permitting evil - not that they show how evil is “necessary.”