Earthly politics
One very quickly deduces by reading this book that Augustine's time was full of chaotic political strife. The basic shape of the book is determined by the various social dysfunctions that have arisen in and around Rome. As the Barbarians learned more and more Latin and moved to the city, the angry citizens began to feel they were being slowly invaded by foreigners. The rift made the city weak to invasion, and before long, they seem to have reached a tipping point. Augustine treats human politics from a religious angle, reminding the reader of first premises.
Pride and humility
The antidote for Rome seems to be humility. Augustine identifies a kind of hubris in the popular Roman idea that their celebration of Christianity didn't work. He says that God is not like the pagan gods which often become the banner of a culture, like a mascot. He says that God is sovereign in a way that is specifically designed to humble a human being, because humans want power and order. No empire had ever attained such power and order as Rome, so they started believing they were invincible, and Augustine sees the fall of Rome as a kind of apocalypse.
Pagan assumption
The content of the book is at sometimes rather puzzling, because Augustine sometimes responds to ideas that the reader might not even have considered believing in. This is the imagery of time affecting our perception of the book; during this time, the earth was widely pagan, and civilization was at a specific turning point in history. The end of paganism is also implied in the fall of Rome, because the survival of Christianity without the unity between Catholicism and Roman politics implies a brand new version of the religion.
The imagery of empire
The imagery of the empire in collapse is helpful to Augustine as an inverted portrait of heaven. In Rome, fear of harm or death made people fearful of foreigners, and that led to fighting that made people very paranoid. Eventually, a collapse takes place, and Augustine uses that as a contrast to heaven. In heaven, there's no reason to ever be paranoid about anything, because no one can kill anyone else. No death means no social chaos, and it means an end to politics done in the name of survival. Augustine treats Rome as an elaborate manifestation of order in the universe as a symbol for the reality to come after death.
