When it comes to introductory courses in religion and theology, the big division isn't a question of faith, but of priorities.
Students want lots of discussion in class sessions and they want to learn facts about religious groups. They also want to become better people. Professors aren't opposed to any of those things, but they are much more interested in teaching critical thinking. While the numbers vary, the gap between students' and professors' goals for these courses is evident at both religious and non-religious institutions.
Winning research support is tough for faculty members in all disciplines -- and makes or breaks careers, especially at research universities. For those in the sciences, competition from many federal agencies has grown more intense in recent years, but there are still billions given out annually and even relatively junior professors can hope to land grants of significant size.