St. Augustine of Hippo (Aurelius Augustinus, 354-430) in his De civitate Dei (City of God, 413-26) explains how each person freely chooses by the quality of his actions to live in one of two cities.
Since God has perfect foreknowledge of all events that will take place in the world, one might ask whether the human will is really free to choose its actions. St. Augustine answers: “We are by no means compelled, either, retaining the prescience of God, to take away the freedom of the will, or, retaining the freedom of the will, to deny that He is prescient of future things. . . . We embrace both. We faithfully and sincerely confess both. The former, that we may believe well; the latter, that we may live well. . . . Consequently, it is not in vain that laws are enacted. . . . Prayers, also, are of avail to procure those things which He foreknew that He would grant to those who offered them; and with justice have rewards been appointed for good deeds, and punishments for sins. For a man does not therefore sin because God foreknew that he would sin.” (V, 10)
Accordingly, writes St. Augustine, two cities have been formed by two loves: the earthly city by the love of self, and the heavenly city by the love of God. “The former, in a word, glories in itself, the latter in the Lord. For the one seeks glory from men; but the greatest glory of the other is God, the witness of conscience. The one lifts up its head in its own glory; the other says to its God, ‘Thou art my glory, and the lifter up of mine head’ (Ps 3:3).”
These two differing attitudes can be seen in the rulers of these two cities. “In the one, the princes and the nations it subdues are ruled by the love of ruling; in the other, the princes and the subjects serve one another in love, the latter obeying, while the former take thought for all. The one delights in its own strength, represented in the persons of its rulers; the other says to its God, ‘I will love Thee, O Lord, my strength’ (Ps 18:1).”
The differing attitudes can also be seen in the sages and saints who populate these two cities. “The wise men of the one city, living according to man, have sought for profit to their own bodies or souls, or both, and those who have known God ‘glorified Him not as God, neither were thankful, but became vain in their imaginations, and their foolish heart was darkened. . . . But in the other city there is no human wisdom, but only godliness, which offers due worship to the true God, and looks for its reward in the society of the saints, of holy angels as well as holy men, ‘that God may be all in all’ (1 Cor 15:28).” (XIV, 28)
Quotations from A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church, Vol. II, ed. Philip Schaff (Edinburgh: T&T Clark, 1886).