To Eustochium
1. “Hear, O daughter, and consider, and incline your ear; forget also your own people and your father's house, and the king shall desire your beauty.” In this forty-fourth psalm God speaks to the human soul that, following the example of Abraham, it should go out from its own land and from its kindred, and should leave the Chaldeans, that is the demons, and should dwell in the country of the living, for which elsewhere the prophet sighs: “I think to see the good things of the Lord in the land of the living.” But it is not enough for you to go out from your own land unless you forget your people and your father's house; unless you scorn the flesh and cling to the bridegroom in a close embrace. “Look not behind you,” he says, “neither stay thou in all the plain; escape to the mountain lest you be consumed.” He who has grasped the plough must not look behind him or return home from the field, or having Christ's garment, descend from the roof to fetch other raiment. Truly a marvellous thing, a father charges his daughter not to remember her father. “You are of your father the devil, and the lusts of your father it is your will to do.” So it was said to the Jews. And in another place, “He that commits sin is of the devil.” Born, in the first instance, of such parentage we are naturally black, and even when we have repented, so long as we have not scaled the heights of virtue, we may still say: “I am black but comely, O you daughters of Jerusalem.” But you will say to me, “I have left the home of my childhood; I have forgotten my father, I am born anew in Christ. What reward do I receive for this?” The context shows— “The king shall desire your beauty.” This, then, is the great mystery. “For this cause shall a man leave his father and his mother and shall be joined unto his wife, and they two shall be” not as is there said, “of one flesh,” but “of one spirit.” Your bridegroom is not haughty or disdainful; He has “married an Ethiopian woman.” When once you desire the wisdom of the true Solomon and come to Him, He will avow all His knowledge to you; He will lead you into His chamber with His royal hand; He will miraculously change your complexion so that it shall be said of you, “Who is this that goes up and has been made white?”
Source: Letters (New Advent)