This is something that has always confused me about Christianity. I hear a lot from Christians that a lot of the evil in the world is the result of the Devil, but how can this be true?

God is supposed to be completely omnipotent, and yet he allows one of his creations to run amok causing torment and misery. Is this all part of the supposed plan?

If it is a part of his plan, then God intended for all of this suffering to occur, however if it is not then the Devil has been able to break away from God to apply his own plan, which means that God is not omnipotent, and the Devil is more powerful than him.

Can someone clear this up for me? I really don't see a way out of this conundrum that ends well for the Christian faith (Or indeed any faith containing both an omnipotent God and a form of Hell or suffering).

PS. I imagine I'll see some responses about free will, however than simply doesn't make sense either. If God is omnipotent, then at the moment of creation he could see every single outcome of every single Earth he could create, yet chose the one that would lead to this happening, asserting that God intended for it to happen.