There is no logical Problem of Evil, because it is impossible in logic for God to create any sort of thing that is not extremely likely to Fall, and so suffer.
God knows perfectly, and so wills, the way that everything should be in order to be best. His existence is necessary, so if he were the only entity, things would necessarily be best.
But God is not the only entity. Because he is necessary, all the other entities that exist must – logically must – be contingent; for, there can be at most one unmoved mover. And contingent beings as such, by definition, are at risk of evil.
That there should be different things, then – that, i.e., there should be more than just one thing, namely God – entails that there should be great risk of evil.
Contingent things might be, or not. I might be at my desk at time t, or not. In the first case, I will be the entity Kristor-at-his-desk-at-t. In the second case, I will be the somewhat different entity Kristor-at-(say)-the-store-at-t. Whichever Kristor actually happens, the other Kristor will not. As the acts that lead to one eventuality must differ from those that lead to the other, so must the chain of facts realized by each of those chains of acts. Each causal chain will result in differences in the population of entities that actually exist.
The existence of any contingent event, or of the possibility of any such event, logically entails the possibility of alternatives to the state of affairs in which it exists. In no other manner could its contingency subsist. Thus for every contingency whatever – for every event or act other than God – there are real alternatives.
So, contingent actuality of any sort entails some degree of freedom in what shall be actualized. Creaturely acts are free per se; this turns out to be just a different way of saying that creatures are contingent. They might or might not become, so they have real options for becoming.
Back then to God’s knowledge of the way that things, including all contingent things, ought ideally to be. That ideal course of events is obviously possible to creatures, or God would not understand it as such. So, the Fall was not necessary: things could really have gone God’s perfect way.
But, being contingent, they could not have been otherwise than to be at risk of going some other way. To be contingent – to be other than God – *just is* to be capable of obeying God’s primordial Will, or not. And every difference between how things would ideally have gone under God’s way and the way that they actually turn out is somewhat evil.
The risk of evil, then, is logically entailed by the fundamental difference between God and creature: that He alone is necessary, while all other things whatsoever are contingent. Are there really differences among things, so that they might turn out differently than they do? Then there is no escape, for any creature whatsoever, from the risk of evil logically inherent in creaturely existence per se.
Finally, this. God could not have created anything at all without accepting the inescapable risk that the contingencies he had brought into being would almost certainly err and Fall, and suffer horribly. But it seems possible that, knowing this quite well, he might have forborne to create anything at all.
The Fall was not, and is not, necessary. But as a matter of mathematics, it is almost infinitely probable. The number of ways things could ideally have gone is one, while the number of ways they might go otherwise is practically infinite.
It’s just math, so God had to know about it. Why then did he see fit to create a world he had to know would Fall? Only because he had to know also that thanks to his almighty provenance it would eventually Rise again, to live with him in bliss forever. The world must die, so we can be sure that there is a limit to suffering. But since it will Rise again to everlasting life (we know that it will because God himself has assured us that he wins in the end), then it will enjoy limitless bliss. The ratio of infinite bliss to any finite amount of suffering is infinity. Only that knowledge of the limitless bliss opened to us as a result of our existence could have justified God’s judgement that the suffering almost certain to result from the world’s creation was warranted.
This calculus enables a fairly confident inference to God’s purpose in creating us – or one of his purposes, anyway – and subjecting us to evil and death: he willed sublime everlasting bliss, enjoyed by countless hosts of immense souls with angelic powers and capacities. He willed infinite Good.