
A milestone in the history of popular theology, The Screwtape Letters is an iconic classic on spiritual warfare and the dynamics of temptation.This profound and striking narrative takes the form of a series of letters from Screwtape, a devil high in the Infernal Civil Service, to his nephew Wormwood, a junior colleague engaged in his first mission on earth, trying to secure the damnation of a young man who has just become a Christian. Although the young man initially looks to be a willing victim, he changes his ways and is "lost" to the young devil.Dedicated to Lewis's friend and colleague J. R. R. Tolkien, The Screwtape Letters is a timeless classic on spiritual conflict and the psychology of temptation which are part of our religious experience
I am not sure Tolkien's books are accurately described as children's books. The Hobbit perhaps, but not the Lord of The Rings IMO.
Though I suspect Lewis would be unhappy to hear that, especially since he wrote a fourth-wall-adjacent bit about devils preferring that humans don't believe in them.
I recommend it even to the non-religious since many of the human errors/temptations it discusses can still be understood through an agnostic lens. For example, one doesn't have to believe whispering devils are involved in order to believe in in/out-group thinking, inferiority complexes, procrastination, etc.
Perhaps he is talking about The Screwtape Letters[0]? I find that book to be awesome stuff. It is definitely Christian moralism, which I could do without, but it is mainly guidance on basic self-appraisal; regardless of the religious (or non-religious) context.