Letters to Malcolm: Chiefly on Prayer.
Reflections on the Intimate Dialogue between Man and God.
Letter XXI. Lewis tackles the irksomeness of prayer. He says the language of the letters makes his prayer life sound way more grand than it really is and that there is no language weak enough to describe his prayer life.Some of that is due to our sins for sure. Some of it might be due to our reluctance to really prayer because God might hear us. It is no good to try for the rich moments in prayer. God will speak to use in his timing and often that is when we are off guard and not expecting it.
Letter XXII. Lewis writes about the supernatural content of Christianity and how it gets him in trouble with liberal Christians. But he defends it as a necessary, even fundamental, part of Christianity. At the end he gives one thoughts on the resurrection of the body.