C. S. Lewis' delightful book The Screwtape Letters presents a series of letters from the demon Screwtape to a younger, less experienced demon named Wormwood. Screwtape offers plenty of advice that Wormwood may use to draw his human “patient” away from God and into the clutches of the devil, but along the way, Screwtape also reveals many important truths about God, humanity, and the world (which is, of course, the whole point).
In the letter containing this quotation, Screwtape explains the nature of human beings as “amphibians—half spirit and half animal.” They are in a constant stay of change, moving between peaks of prosperity and good feeling and troughs of poverty and dryness in both their physical and spiritual selves. God, whom Screwtape refers to as the “Enemy,” makes use of the troughs even more than the peaks, because the troughs help people become more fully themselves through their free choices and responses to suffering and difficulties.
Screwtape goes on to explain that God does not want a bunch of mindless robots, but a bunch of “little replicas of Himself” who choose to conform their wills to His own. The devil, on the other hand, (whom Screwtape calls “Our Father Below”) merely wants to devour human beings and suck them into himself and his own misery. He does not want people to be free individuals.
God, though, Screwtape continues, wants people to be freely united to Him but still distinct individuals. He will not “override a human will,” and He sometimes allows people to experience the troughs, difficulties, sufferings, and dryness so they will turn to Him in faith and with their wills rather than merely for the pleasant feelings they may have. This way, people grow stronger in love (which is an act of will far more than a feeling) and closer to Him.