It's an heresy for the Abrahamic religions to say that the Devil is as strong as God, iirc. So Box is right to say that the evil in the world is the fault of God, if only indirectly.
On the subject of finite things being the only ones that man can understand, and without trying to be snarky, I think we should remember that maths and numbers are infinite, and that doesn't keep people from studying, working, and understanding them.