Garry Wills is known for the extraordinary quality of his observations and the mastery of primary sources that has defined all of his work. But it is his encyclopedic knowledge of the history of religion in this country that informs this particular work and makes it so compelling.
Augustine saw a collaborative relationship between faith and reason. He believed there are two kinds of knowledge. One is based on belief or faith. The other relies on things observed (reason) and is called understanding. Knowledge based on faith comes from God; it always has an authority that knowledge based on reason cannot possess.