Meaning of Letter 8

The Screwtape Letters is a satirical work, and determining the meaning of any particular letter requires some reading between the lines. Screwtape and Wormwood are demons, so the advice the former is giving clearly can't be taken at face value; instead, we need to cut through his point of view to find the larger claim(s) that C. S. Lewis is making about the nature of God, Christianity, etc.

With that in mind, Letter 8 is a response to Wormwood's claim that the man he has been charged with tempting is losing his faith (or, at least, becoming less enthusiastically religious). Screwtape, however, cautions Wormwood that he should not take this as a sign of success, because, "the Enemy"—that is, God—"relies on the troughs [of faith] even more than on the peaks." This, then, is the main subject of Letter 8, with Screwtape disgustedly explaining the apparent paradox in terms of free will. Because God wants humans to come to him by choice, it would be counterproductive to be constantly and viscerally present in their lives.

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...For His ignoble idea is to eat the cake and have it; the creatures are to be one with Him, but yet themselves; merely to cancel them, or assimilate them, will not serve.

Ultimately, then, Letter 8 is both a defense of spiritual dry periods and an argument about the kind of life people have "in God." Feeling God's absence but still adhering to Christian precepts is actually a kind of faith itself, since it involves freely choosing belief. For that reason, the end result of faith is not less freedom but more freedom, and a fuller sense of one's own identity and purpose.