About the book (from Wikipedia):
The Screwtape Letters is a Christian apologetic novel written by C. S. Lewis. It is written in a satirical, epistolary style and while it is fictional in format, the plot and characters are used to address Christian theological issues, primarily those to do with temptation and resistance to it. First published in February 1942, the story takes the form of a series of letters from a senior Demon Screwtape to his nephew Wormwood, a Junior Tempter. The uncle’s mentorship pertains to the nephew’s responsibility for securing the damnation of a British man known only as “the Patient”.
About C. S. Lewis (from Wikipedia):
Clive Staples Lewis, commonly known as C. S. Lewis (29 November 1898 – 22 November 1963), was a novelist, poet, academic, medievalist, literary critic, essayist, lay theologian, broadcaster, lecturer, and Christian apologist. Born in Belfast, Ireland, he held academic positions at both Oxford University (Magdalen College), 1925–54, and Cambridge University (Magdalene College), 1954–63. He is best known for his fictional work, especially The Screwtape Letters, The Chronicles of Narnia, and The Space Trilogy, and for his non-fiction Christian apologetics, such as Mere Christianity, Miracles, and The Problem of Pain.