If you've never read "Screwtape" ...

Casey Cep explains "Why Readers Love The Screwtape Letters", and why its fans are not limited to Christian believers:

.... Continuously in print since Lewis published it in 1942, the novel has been adapted into plays, made into a comic book, and recorded as an audio drama by John Cleese. Fox owns the film rights, and Ralph Winter, best known for blockbusters like “X-Men” and “Fantastic Four,” has said he will produce it. Three years ago, I saw one of the stage adaptations in New York, where it was shockingly difficult to get a ticket. I remember wondering then, as I have been again since Justice Scalia’s interview, why the novel is still so popular.

Its appeal, I think, comes from Lewis’s success in writing a theodicy of the everyday. .... “The Screwtape Letters” features a senior demon called Screwtape writing thirty-one letters of advice and encouragement to his inexperienced nephew, Wormwood, who is trying to win the soul of a nameless young man. ....

He wants nothing but the best for his nephew, an erring neophyte unversed in the finer methods of temptation. Screwtape is more than just a masterful theologian—he is a careful anthropologist. “When two humans have lived together for many years,” he tells his nephew, “it usually happens that each has tones of voice and expressions of face which are almost unendurably irritating to the other. Work on that.” Adultery seems excessive when furrowed eyebrows and dismissive tones can do the work of ruining relationships slowly: “Courtship is the time for sowing those seeds which grow up ten years later into domestic hatred.” ....

The greatest of these vice-for-virtue deceptions was achieved, Screwtape says, by “the admirable work of our Philological Arm in substituting the negative unselfishness for the Enemy’s positive Charity.” Couples are ideal for getting patients to resent the very individuals they most desired to show charity:

In discussing any joint action, it becomes obligatory that A should argue in favour of B’s supposed wishes and against his own, while B does the opposite. It is often impossible to find out either party’s real wishes; with luck, they end by doing something that neither wants, while each feels a glow of self-righteousness and harbours a secret claim to preferential treatment for the unselfishness shown and a secret grudge against the other for the ease with which the sacrifice has been accepted.

Another way of framing such failed virtues is to say that true temptation distracts from the present and directs to the future. Instead of appreciating your boyfriend’s preference for one television show over another or your wife’s desire to go for a walk instead of staying at home, you worry unsustainably about being the most unselfish of partners or scoring more points than your wife on the balance sheet of the relationship. “Gratitude looks to the past and love to the present,” Screwtape tells Wormwood, but “fear, avarice, lust, and ambition look ahead.” It’s perfect satire. ....

For believers, the letters are theology in reverse, teaching the love of God through the wiles of the Devil, but for all readers, regardless of belief, the letters frame human experience as a familiar sequence of trials, from how you take your tea and what parties you attend to the sort of person you choose for a partner and the sort of politics you espouse. As Justice Scalia said when he invoked “The Screwtape Letters,” “That’s a great book. It really is, just as a study of human nature.” The novel remains wildly popular because whether or not you agree with Lewis and Scalia that the Devil is real, the evils promoted by Screwtape—greed, gluttony, pride, envy, and violence—most certainly are. [more]

The Devil You Know: Why Readers Love 'The Screwtape Letters' : The New Yorker