From Letter 4 of The Screwtape Letters:
The humans do not start from that direct perception of Him which we, unhappily, cannot avoid. They have never known that ghastly luminosity, that stabbing and searing glare which makes the background of permanent pain to our lives. If you look into your patient's mind when he is praying, you will not find that. If you examine the object to which he is attending, you will find that it is a composite object containing many quite ridiculous ingredients. There will be images derived from pictures of the Enemy as He appeared during the discreditable episode known as the Incarnation: there will be vaguer-perhaps quite savage and puerile-images associated with the other two Persons. There will even be some of his own reverence (and of bodily sensations accompanying it) objectified and attributed to the object revered. I have known cases where what the patient called his "God" was actually located-up and to the left at the corner of the bedroom ceiling, or inside his own head, or in a crucifix on the wall. But whatever the nature of the composite object, you must keep him praying to it-to the thing that he has made, not to the Person who has made him. You may even encourage him to attach great importance to the correction and improvement of his composite object, and to keeping it steadily before his imagination during the whole prayer. For if he ever comes to make the distinction, if ever he consciously directs his prayers "Not to what I think thou art but to what thou knowest thyself to be", our situation is, for the moment, desperate.