3 A truce to the calumnies which the malice of backbiters continually fastens upon all who call themselves Christians to keep them through fear of shame from aspiring to virtue. Except by letter we have no knowledge of each other; and where there is no knowledge after the flesh, there can be no motive for intercourse save a religious one. “Honour your father,” the commandment says, but only if he does not separate you from your true Father. Recognize the tie of blood but only so long as your parent recognizes his Creator.
Should he fail to do so, David will sing to you: “hearken, O daughter, and consider, and incline your ear; forget also your own people and your father's house. So shall the king greatly desire your beauty, for he is your Lord.” Great is the prize offered for the forgetting of a parent, “the king shall desire your beauty.” You have heard, you have considered, you have inclined your ear, you have forgotten your people and your father's house; therefore the king shall desire your beauty and shall say to you:— “you are all fair, my love; there is no spot in you.” What can be fairer than a soul which is called the daughter of God, and which seeks for herself no outward adorning. She believes in Christ, and, dowered with this hope of greatness makes her way to her spouse; for Christ is at once her bridegroom and her Lord.
Source: Letters (New Advent)