17 The other is concerned with the soul, which comes from God and is divine, and partakes of the heavenly nobility, and presses on to it, even if it be bound to an inferior nature. Perhaps indeed there are other reasons also for this, which only God, Who bound them together, and those who are instructed by God in such mysteries, can know, but as far as I, and men like myself can perceive, there are two: one, that it may inherit the glory above by means of a struggle and wrestling with things below, being tried as gold in the fire by things here, and gain the objects of our hope as a prize of virtue, and not merely as the gift of God. This, indeed, was the will of Supreme Goodness, to make the good even our own, not only because sown in our nature, but because cultivated by our own choice, and by the motions of our will, free to act in either direction. The second reason is, that it may draw to itself and raise to heaven the lower nature, by gradually freeing it from its grossness, in order that the soul may be to the body what God is to the soul, itself leading on the matter which ministers to it, and uniting it, as its fellow-servant, to God.
Source: Orations (New Advent)