So much for Nature's imperfection; her positive depravity calls for a very different explanation. According to the Christians this is all due to sin: the sin both of men and of powerful, non-human beings, supernatural but created... To be sure, the morbid inquisitiveness about such beings which led our ancestors to a pseudo-science of Demonology, is to be sternly discouraged: our attitude should be that of the sensible citizen in wartime who believes that there are enemy spies in our midst but disbelieves nearly every particular spy story. We must limit ourselves to the general statement that beings in a different, and higher 'Nature' which is partially interlocked with ours have, like men, fallen and have tampered with things inside our frontier. The doctrine, besides proving itself fruitful of good in each man's spiritual life, helps to protect us from shallowly optimistic or pessimistic views of Nature. To call her either 'good' or 'evil' is boys' philosophy. We find ourselves in a world of transporting pleaures, ravishing beauties, and tantalising possibilities, but all constantly being destroyed, all coming to nothing. Nature has all the air of a good thing spoiled.
The sin, both of men and of angels, was rendered possible by the fact that God gave them free will: thus surrendering a portion of His omnipotence (it is again a deathlike or descending movement) because He saw that from a world of free creatures, even though they fell, He could work out (and this is the reascent) a deeper happiness and a fuller splendour than any world of automata would admit.
C.S. Lewis, Miracles (1947)