Is the devil real? Here is Msgr. Ronald Knox on that: “It is stupid of modern civilization to have given up believing in the devil, when he is the only explanation of it.” Monsignor Knox, eminent British convert, author, retreat master and translator of the Bible, may have been indulging in irony. But irony doesn’t change the fact that the devil and his demonic associates exist. I came across the Knox quote in Manual for Spiritual Warfare, newly published by Tan Books and edited by Paul Thigpen. “Like it or not,” Thigpen begins his thoughtful introduction, “You are at...