(Please note that in The Screwtape Letters, Lewis is playing devil's advocate and is, in fact, writing as a senior devil, Screwtape, to his understudy devil, Wormwood. Therefore, everything is reversed. The patient therefore, is us. Their "Enemy" is Jesus. Our Friend.)
Your patient will, of course, have picked up the notion that he must submit with patience to the Enemy's will. What the Enemy means by this is primarily that he should accept with patience the tribulation which has actually been dealt out to him—the present anxiety and suspense. It is about this that he is to say "Thy will be done", and for the daily task of bearing this that the daily bread will be provided. It is your business to see that the patient never thinks of the present fear as his appointed cross but only of the things he is afraid of.
Let him regard them as his crosses: let him forget that, since they are incompatible, they cannot all happen to him, and let him try to practice fortitude and patience to them all in advance. For real resignation, at the same moment, to a dozen different and hypothetical fates, is almost impossible, and the Enemy does not greatly assist those who are trying to attain it: resignation to present and actual suffering, even where that suffering consists of fear, is far easier and is usually helped by this direct action.
The Screwtape Letters, by C. S. Lewis
We are to submit, with patience, to the Father's will. But the fears and terrors of the night have nothing to do with His will. He will give grace, daily bread, for each actual need or trial.
"Therefore, do not be anxious about tomorrow, for tomorrow will be anxious for itself. Sufficient for the day is its own trouble."
As an aside, while it is important to know your enemy, it is of endlessly greater importance to know your Champion. If you know Christ, then no plan of the enemy can triumph.