What is the theme in Staying Fat for Sarah Byrnes by Chris Crutcher?

One of Moby's classmates is a Christian who brings his religious beliefs into every discussion in which he is included. This young man, Mark Brittain, feels that a Christian is someone who lives a perfect life and makes no mistakes. Mark also believes that he is destined to spread the word, that his life is a mission to bring more people into the bosom of Christianity. Mark's plan did not make room for his girlfriend to become pregnant. Mark blames the girl and forces her to have an abortion despite the fact that abortion is strictly against his beliefs. Mark believes his mission is too important to be side railed by an illegitimate child and that he is above the simple man who would be damned for committing this sin.