Augustine defines peace at every level of reality, from the body to the cosmos. Bodily peace is the right arrangement of its parts. The peace of the irrational soul is the settled repose of its appetites. Rational peace is the harmony of knowledge and action. Social peace is concord between persons. Political peace is the ordered concord of citizens. And the peace of the city of God is the perfectly ordered enjoyment of God and one another in God. Each is a real form of peace, but they are not equal — they are ordered toward one another, each a lower image of the highest.
What is the supreme good? The philosophers had disagreed for centuries. Augustine's answer is direct: the supreme good is eternal life — not survival, but the full flourishing of the soul in uninterrupted union with God. This is not a retreat from philosophy; it is the answer that philosophy's own best reasoning demands, once it is rescued from the assumption that the highest good must be attainable in this life. The city of God's answer to the philosophers is that their accounts of happiness fail because they seek a lasting good in a world where nothing lasts.
The city of God does not despise earthly peace. On the contrary, Augustine insists that the pilgrim community uses earthly peace — it values stable government, settled laws, the suppression of violence — precisely because these things enable it to pursue its true end without constant disruption. The earthly city and the city of God share the same interest in civic order; they differ only in what they make of it. For the earthly city, peace is the final good. For the city of God, it is an instrument on the road to a higher peace.
This means Augustine is not a political quietist. He does not tell Christians to withdraw from civic life — he tells them to live in it rightly, using its goods without being enslaved to them, seeking its peace without mistaking it for their home. The Christian in the world is like a traveller who sleeps in an inn: grateful for shelter, but not deceived into thinking the inn is where he belongs.
The great peace passage appears in Book XIX, chapter 13. The treatment of the supreme good occupies most of the book's opening chapters, and Augustine's engagement with Varro's 288 philosophical sects provides the philosophical frame for the whole discussion.