Christian music and especially Christian rock is a world of its own, a self-contained universe that mirrors the trends and styles of the mainstream. But how does it work? And what can it tell us about the interactions between audiences and industries that structure popular music? We talk to Andrew Mall, the author of “God Rock Inc.: The Business of Niche Music” to explore everything from the Jesus People to Christian Metalcore, while discussing how the complex relationship between sacred and secular pop can help us understand the ethics, aesthetics, and boundaries that define musical genre.