I promised you more about participation, so here's my first attempt to make good on that pledge. One of the big questions in theology is that of the nature of evil: what is it? How can it come to be in the good world God made? When you start to say that existence is a predicate of God, and that therefore insofar as anything exists, you start to force yourself towards a particular answer to that question, and so a lot of patristic theologians argue for some sort of concept of evil not as a thing in itself, but as a deprivation of the good.
Pseudo-Dionysius the Areopagite is a good example of this, so I'll start by introducing you and then talk a bit about what he says. He's called Pseudo-Dionysius because he writes as if he's the Dionysius who is mentioned in Acts 17:34, someone who converted to Christianity after Paul's sermon in Athens about the unknown God. But he was probably actually writing in 5th century Syria. He was incredibly influential in theology, particularly in the West, even though not many people have heard of him these days. He's particularly famous for his mystical/apophatic theology, which is about the limitations of language when talking about God, but also gets into the discussion about the nature of evil.
He says that, because everything that exists gets its being from God, evil can't produce beings or give birth - instead it's good that has got broken, misdirected, twisted in some way. Evil is good gone wrong, not a thing in itself. That means that nothing can be evil by nature - even the demons aren't inherently evil, but are evil because of the ways they fall short of the good. There's no such thing as pure evil, because evil depends on the good for its very existence. It's a parasite - any power it has, any existence, any intelligence, any will - it gets from the good and distorts. One of the characteristics of God is stability: he is always who he is, and his goodness never changes, never grows or shrinks, and so evil can't even have stability except inasmuch as it gets it from the good.
This solves quite neatly on of the big theological problems of evil - how can there be something that God didn't create (answer: because evil doesn't be as such), and feels in a lot of ways like quite a satisfying way of thinking about it, but here's what seems to me to be an issue: if evil isn't a thing as such, and nothing can be inherently and stably evil, then does that mean that even Satan can be redeemed? Answers on a postcard.