Writing to his friend Arthur Greeves in 1933, C. S. Lewis offered these thoughts on the nature of good and evil:
I think one may be quite rid of the old haunting suspicion—which raises its head in every temptation—that there is something else than God—some other country . . . into which He forbids us to trespass—some kind of delight wh. He “doesn’t appreciate” or just chooses to forbid, but which wd. be real delight if only we were allowed to get it.
The thing just isn’t there.
Whatever we desire is either what God is trying to give us as quickly as He can, or else a false picture of what He is trying to give us . . . wh. would not attract us for a moment if we saw the real thing. . . .
Only because He has laid up real goods for us to desire are we able to go wrong by snatching at them in greedy, misdirected ways. The truth is that evil is not a real thing at all, like God. It is simply good spoiled. That is why I say there can be good without evil, but no evil without good.
You know what the biologists mean by a parasite—an animal that lives on another animal. Evil is a parasite. It is there only because good is there for it to spoil and confuse.
I believe Lewis is accurate in what he says here. Sin is always the selfish ruination of something good God offers. Food, used in the way God intended, is great. Food abused is gluttony. Sex as a means of love, commitment, and the creation of a family is a blessing; sex abused is a lustful trap that ruins lives. There is a proper kind of pride—satisfaction for a job well done—that is twisted into arrogance when selfishness takes over. There is nothing good that can’t be perverted into evil. That’s what sin is all about.
What God is all about is delivering us from that sinfulness, thereby putting every good thing back in its proper place where it can be enjoyed in the way He intended.