A common theme I found while reading through The Screwtape Letters is Lewis's belief in both mystical and spiritual as well as very practical and present parts of Christianity. You cannot accept one but neglect the other. In the third letter Screwtape addresses how to twist the patient's prayer so it is rendered innocuous. He proposes that by keeping the patient's prayer life much too heavily focused on the spiritual side of life, they lose the meaning because he is not addressing the everyday, here-and-now problems that he and those he loves are facing. This idea is along the same string of though as his definition of prayer in his Letters to Malcolm. There he talks of prayer as being an unveiling of ourselves to God (not that God's sight is hindered in any way). By focusing too much on the spiritual side of a person's existence you lose much of what is actually on your mind and therefor your prayer life suffers.