He tells Wormwood that it is best for the young man to be an extremist -- and to be extreme at anything, in whichever direction -- because in doing so there is a lack of temperance which alienates oen from God and makes one susceptible to the machinations of distractions. These temptations fail for a variety of reasons. One is due to the power of the love of God, which sustains the young Christian through virtually all of his travails and triumphs, as well. Yet there are certain events that take place that fortify his faith. One of these is his relationship with a Christian woman, as opposed to the lewd one Screwtape is hoping he falls for. Also, his early death helps to bring the patient closer to God as well.

Screwtape's relationship with Wormwood is actually emblematic of the devil's relationship with mankind. Screwtape is nice to Wormwood and friendly to him so long as Wormwood serves his purpose in corrupting man or the patient as the young man whom Wormwood is assigned to in C.S. Lewis' the Screwtape Letters. Once Screwtape's interest in Wormwood is complete -- which is signified in the novel by Wormwood's failure to corrupt the patient and the patient's impending arrival in heaven -- Screwtape has no more use for him and treats him accordingly by talking to him despairingly and preparaing to harm him.

Wormwood largely regards Screwtape in the same way; the former needs the latter to help him learn his craft of debauchery. Thus, they have a conventional mentor-student relationship. Over the course of the book, this relationship changes because both demons are only concerned with pursuing their own goals. Thus, Wormwood snitches about Screwtape's positive remark about God, and Screwtape in turn is only to ready to have Wormwood devoured due to his failure to corrupt the patient.
Such a relationship, of course, is the inverse of God's relationship with man. God genuinely cares for man and grows closer to him and helps him more when there is adversity. Screwtape and Wormwood do the opposite. At the first sign of things going wrong or any opportunity to further their own aims and counteract that of the other, they readily backstab one another. God never does this to man, and is willing to forgive and offer him another chance. By having Screwtape preparing to devour Wormwood at the end of the story, Lewis is suggesting the parasitic nature of evil and the fact that it does not have lasting principles or virtues.

Works Cited

Lewis, C.S. The Screwtape Letters. New York: HarperOne. 2009. Print.