Two loves, then, have made two cities. Love of self, even to the point of contempt for God, made the earthly city, and love of God, even to the point of contempt for self, made the heavenly city. Thus the former glories in itself, and the latter glories in the Lord. The former seeks its glory from men, but the latter finds its highest glory in God, the witness of our conscience. The former lifts up its head in its own glory; the latter says to its God, My glory, and the one who lifts up my head (Ps. 3:3). In the former the lust for domination dominates both its princes and the nations that it subjugates; in the latter both leaders and followers serve one another in love, the leaders by their counsel, the followers by their obedience. The former loves its own strength, displayed in its men of power; the latter says to its God, I love you, O Lord, my strength (Ps. 18:1).
The earthly city, which does not live by faith, seeks an earthly peace, and it establishes a concord of command and obedience among its citizens in order to bring about a kind of accommodation among human wills with regard to the things that pertain to this mortal life. And the heavenly city – or rather, that part of it which is on pilgrimage in this mortal existence and which lives by faith – must of necessity make use of this peace as well, at least until this mortal existence, for which such peace is necessary, passes away. …
So long as this heavenly city is a pilgrim on earth, then, it calls forth citizens from all peoples and gathers together a pilgrim society of all languages. It cares nothing about any differences in the manners, laws, and institutions by which earthly peace is achieved or maintained. But it does not rescind or abolish any of these; rather, it preserves and follows them, provided only that they do not interfere with the religion which teaches that we are to worship the one supreme and true God, for, however different they may be in different nations, they all aim at one and the same thing – earthly peace. Thus, even the heavenly city makes use of earthly peace during its pilgrimage.
Source: William Babcock, trans. The City of God (De Civitate Dei) XI–XXII (New City, 2013) 136–137, 375.