On free will
The sin, both of men and of angels, was rendered possible by the fact that God gave them free will: this 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 re-ascent) a deeper happiness and a fuller splendour than any world of automata would admit.
Miracles: A Preliminary Study. Copyright 1947 C. S. Lewis Pte. Ltd. Copyright renewed © 1947 C. S. Lewis Pte. Ltd. Revised 1960, restored 1996 C. S. Lewis Pte. Ltd. All rights reserved. Used with permission of HarperCollins Publishers. Words to Live By: A Guide for the Merely Christian. Copyright © 2007 by C. S. Lewis Pte. Ltd. All rights reserved. Used with permission of HarperCollins Publishers.