The City of God is a religious, political, and philosophical dissertation on the fall of Rome. In this work, divided into twenty-two books, Augustine argues against claims that Christianity caused Rome to fall as he addresses the social and political climate of Rome and events of the time (410 BCE). Augustine proposes that Christianity actually helped Rome survive.

Augustine describes the existence of two groups or sub-cities, "The City of God" (believers, the elect) and "The City of Man" (non-believers, pagans), at odds with one another in Rome and society in general. Augustine explains that since the fall of angels in the beginning of time, these two groups have contended for the souls of man everywhere, and these forces continue the fight over the hearts and souls of Romans.

Each of the twenty-two books addresses a spiritual aspect related to the condition of man in relation to God.

For instance, in his first book of the series, Augustine addresses non-Christians who sought shelter and protection in the Christian churches of Rome but then claimed that Christians were to blame for Rome being attacked. He explains to all that injustice does fall upon the unrighteous and righteous.

However, in book two, Augustine does boldly state that, as people of Rome worshiped pagan gods, not the one, true God, they allowed moral corruption into the city. Augustine argues that these pagan gods did not stop the attacks in Rome, in his third book. In books four and five, Augustine explains how Christianity actually benefited Rome.

Next, in books six through ten, Augustine provides a strong defense of Christ being the only answer for salvation, peace, and reconciliation with God as he criticizes pagan beliefs.

Then, in the rest of the books in the series, Augustine discusses The City of God specifically as he references many areas of the Bible, in both the Old Testament and New Testament.

At the end, Augustine provides hope for those who seek to follow Christ by pointing to eternal salvation through Christ.