Lewis, C. S. Letters to Malcolm, Chiefly on Prayer.
This book serves several functions. In it Lewis goes a bit deeper in theology than what you find in Mere Christianity and he also touches on explosive issues in mid-century Anglican theology.
He covers basic issues as man-made prayers, bodily posture, distractions and the problem of having non-images in the head while praying. He notes the dangers and possible value in some of these.
Some of the real theological gems are at the end. Should we pray to God for the saints? Like a good Anglican, Lewis doesn’t tell you what you *should* do. But he has some interesting points: most of the people I love are already dead? Am I forbidden to mention them to God because they are dead? And while it is true that we can’t pray others into heaven from hell, because it is already fixed, Lewis points out that if we apply that same reason to prayer because of predestination, we are in the same bind. Why pray, since it is already fixed in eternity?
Lewis rejects the crude literal version of purgatory and where earlier Romish divines like More went astray. While I agree with Lewis that there are post-death moments which aren’t quite heaven or hell, I don’t think his reasons for Purgatory–however he defines it–are compelling.
He ends on an outstanding discussion of the Resurrection of the body and the nature of matter and sensory experience.