A letter from the demon Screwtape to his nephew Wormwood, regarding the peaks and troughs in human life:
“You must have often wondered why the Enemy [God] does not make more use of His power to be sensibly present to human souls in any degree He chooses and at any moment. But you now see that the Irresistible and the Indisputable are the two weapons which the very nature of His scheme forbids Him to use. Merely to override a human will (as His felt presence in any but the faintest and most mitigated degree would certainly do) would be for Him useless. He cannot ravish. He can only woo. . . .
“He leaves the creature to stand up on its own legs — to carry out from the will alone duties which have lost all relish. It is during such trough periods, much more than during the peak periods, that it is growing into the sort of creature He wants it to be. Hence the prayers offered in the state of dryness are those which please Him best.”
C. S. Lewis, The Screwtape Letters (New York: HarperCollins, 2000), 39-40.