Published in 1942, The Screwtape Letters by C.S. Lewis is indubitably an insightful satire, at times convicting, and I would argue that it is a must read for every Christian.

The book is written in epistolary form where an older and more experienced demon named Screwtape writes letters to his younger, inexperienced nephew (also a demon) training him how to win the souls of men.

Here, I summarize, as I understand them, a couple thoughts discussed in chapters 1, 2, and 8 through Screwtape's letters to his nephew:
-- If humans focus on earthly things, they'll lose sight of the heavenly and eternal
-- Relying on human emotion and experience instead of relying on the Word of God is a recipe for disaster for humans but a win for the devil
-- Depending on the Word of God is key to resist the devil
-- The devil uses our peaks (strong points in life) to get us away from God, while God uses our lows to bring us closer to Him.