It is often asked: If there is God, He can everything and He is good, then why evil exists?
The only possible answer is that evil is necessary, that is absolute good is impossible without evil.
My supposed answer to this is the following possible argument:
The only mean to prevent evil in the future is remembrance of evil in the past. This follows that evil in the past is necessary (unless we would allow false memory of past evil, but false memory is an evil itself).