Throughout the course of humanity, no religion has had an easy time getting started and gaining followers. While that's certainly true, it's hard to envision a greater struggle than that of the Catholic Church. Its thousands of conversions go hand in hand with torture, imprisonment, and martyrs.

In the early days, when Catholics refused to worship the Roman gods, those in power did all they could to destroy the church. Violence was rampant among Christians. Theological differences, illness, leadership changes, and death all left their mark with time.

John F. Fink seeks to...