My dear Wormwood,

If you do not know what 'The Screwtape Letters' are...

Wormwood: a junior tempter in Satan's army
Screwtape: Wormwoods uncle, an experienced tempter with much advice and many grand examples of keen tempting, for his nephew to learn from.
The Enemy: God
The patient: the human that Wormwood has been assigned to; Wormwood is to ensure his patient does not wander too close to the Enemy (God), or ever truly become one of His.

Wormwood's patient has previously converted to Christianity, but is now enduring his first "slump"...here we find Screwtape's advice for Wormwood...

My dear Wormwood,
Obviously you are making excellent progress. My only fear is lest in attempting to hurry the patient you awaken him to a sense of his real position. For you and I, who see that position as it really is, must never forget how totally different it ought to appear to him. We know that we have introduced a change of direction in his course which is already carrying him out of his orbit around the Enemy; but he must be made to imagine that all the choices which have affected this change of course are trivial and revocable. He must not be allowed to suspect that he is now, however slowly, heading right away from the sun on a line which will carry him into the cold and dark of utmost space.
For this reason I am almost glad to hear that he is still a churchgoer and a communicant. I know there are dangers in this; but anything is better than that he should realise the break he has made with the first months of his Christian life. As long as he retains externally the habits of a Christian he can still be made to think or himself as one who has adopted a few new friends and amusements but whose psiritual state is much the same as it was six weeks ago. And while he thinks that, we do not have to contend with the explicit repentance of a definite, fully recognised, sin, but only with his vague, though uneasy, feeling that he hasn't been doing very well lately.
This dim uneasiness needs careful handling. If it gets too strong it may wake him up and spoil the whole game. On the other hand, if you supress it entirely - which, by the by, the Enemy will probably not allow you to do - we lose an element in the situation which can be turned to good account. If such a feeling is allowed to live, but not alowed to become irresistible and flower into real repentance, it has one invaluable tendency. It increases the patient's reluctance to think about the Enemy. All humans at nearly all times have some such reluctance; but when thinking of Him involved facing and intensifying a whole vague cloud of half-conscious guilt, this reluctance is increased tenfold. They hate every idea that suggests Him, just as men in financial embarassment hate the very sight of a pass-book. In this state your patient will not omit, but he will increasingly dislike, his religious duties. He will think about them a little as he feels he decently can beforehand, and forget them as soon as possible when they are over. A few weeks ago you had to tempt him to unreality and inattention in his prayers: but not you will find him opening his arms to you and almost begging you to distract his purpose and benumb his heart. He will want his prayers to be unreal, for he will dread nothing so much as effective contact with the Enemy. His aim will be to let sleeping worms lie.
As this condition becomes more fully established, you will be gradually freed from the tiresome business of providing Pleasures as temptations. As the uneasiness and his reluctance to face it cut him off more and more from all real happiness, and as habit renders the pleasures of vanity and excitement and flippancy at once less pleasant and harder to forgo (for that is what habit fortunately does to a pleasure) you will find that anything or nothing is sufficient to attract his wandering attention. You no longer need a good book, which he realy likes, to keep him from his prayers or his work or his sleep; a column of advertisements in yesterday's paper will do. You can make him waste his time not only in conversations he enjoys with people whom he likes, but in conversations with those he cares nothing about on subjects that bore him. You can make him do nothing at all for long periods. You can keep him up late at night, not roistering, but staring at a dead fire in a cold room. All the healthy and out-going activities which we want him to avoid can be inhibited and given in return, so that at least he may say, as one of my own patients said on his arrival down here, 'I now see that I spent most of my life in doing neither what I ought nor what I liked.' The Christians describe the Enemy as one 'without whom Nothing is strong'. And Nothing is ery strong: strong enough to steal away a man's best years not in sweet sins but in dreary flickering of the mind over it knows not what and knows now why, in the gratification of curiousities so feeble that the man is only half aware of them, in drumming of fingers and kicking of heels, in whistling tunes that he does not like, or in the long, dim labyrinth of reveries that have not even lust or ambition to give them a relish, but which, once chance association has started them, the creature is too weak and fuddled to shake off.
You will say that these are very small sins; and doubtless, like all young tempters, you are anxious to be able to report spectacular wickedness. But do remember, the only thing that matters is the extent to which you separate the man from the Enemy. It does not matter how small the sins are provided that the cumulative effect is to edge the man away from the Light and out into Nothing. Murder is no better than cards if cards will do the trick. Indeed the safest road to Hell is the gradual one - the gentle slope, soft underfoot, without sudden turnings, without milestones, without signposts...

Your affectionate uncle,
Screwtape

The Screwtape Letters
By C.S. Lewis