It shines light on the subtleties that evil has on man and the ways in which Satan tempts us. 

Below are two excerpts that stand out to me. The first being a moment in the novel that explained how spirits are sometimes defined as forces, which minimizes the conscious power they evoke. 

The second describes the distinct characteristics of God versus that of evil.

Note that since the novel is written from evil’s point of view, “Enemy” here means God.

“If once we can produce our perfect work—the Materialist Magician, the man, not using, but veritably worshipping, what he vaguely calls “Forces” while denying the existence of “spirits”—then our final victory will be in sight. But in the meantime we must obey our orders. I do not think you will have much difficulty in keeping the patient in the dark. The fact that “devils” are predominantly comic figures in the modern imagination will help you. If any faint suspicion of your existence begins to arise in his mind, suggest to him a picture of something in red tights, and persuade him that since he cannot believe in that (it is an old textbook method of confusing them) he therefore cannot believe in you. ”

Excerpt From: C. S. Lewis. “The Screwtape Letters (Enhanced Special Illustrated Edition).” iBooks. https://itun.es/us/Pckuz.l

“But the obedience which the Enemy demands of men is quite a different thing. One must face the fact that all the talk about His love for men, and His service being perfect freedom, is not (as one would gladly believe) mere propaganda, but an appalling truth. He really does want to fill the universe with a lot of loathsome little replicas of Himself—creatures whose life, on its miniature scale, will be qualitatively like His own, not because He has absorbed them but because their wills freely conform to His. We want cattle who can finally become food; He wants servants who can finally become sons. We want to suck in, He wants to give out. We are empty and would be filled; He is full and flows over. Our war aim is a world in which Our Father Below has drawn all other beings into himself: the Enemy wants a world full of beings united to Him but still distinct.”