In 1500 Christians knew that God gave them the church to shepherd believers toward salvation and that it was centered at Rome and ruled by a pope. Today, that church is but one of forty thousand Christian denominations, each with distinctive structures and doctrines. How did this happen? Then, as now, all aspects of the church--from its divine mission to its offices and operations, hierarchy, and bureaucracy--were of interest to theologians, thinkers, and troublemakers alike, but for ages there had been satisfaction with the status quo. In the late Renaissance this gave way to frustration and...