Why does Les sometimes go against his denominational background?
The teacher sometimes crosses his own denominational background because he is committed to a non-denominational approach and must go by what the Book says, not by what someone taught him to say it says. He aims to teach the Bible rather than preach or impress.
Les explains that the class is informal and non-denominational. He says they are not there to preach at anybody, scream, or holler, but simply to teach the Book. Although this stance may sometimes cross positions from his own background, he cannot help it, because he has to go by what the Book says, and not what someone has taught him to say that it says. The goal is to impress people with the Bible alone, not with themselves.