30 Since, then, all these excellent precepts of the Lord, which Faustus tries to prove to be contrary to the old books of the Hebrews, are found in these very books, the only sense in which the Lord came not to destroy the law, but to fulfill it, is this, that besides the fulfillment of the prophetic types, which are set aside by their actual accomplishment, the precepts also, in which the law is holy, and just, and good, are fulfilled in us, not by the oldness of the letter which commands, and increases the offense of the proud by the additional guilt of transgression, but by the newness of the Spirit, who aids us, and by the obedience of the humble, through the saving grace which sets us free. For, while all these sublime precepts are found in the ancient books, still the end to which they point is not there revealed; although the holy men who foresaw the revelation lived in accordance with it, either veiling it in prophecy as suited the time, or themselves discovering the truth thus veiled.
Source: Reply to Faustus the Manichaean (New Advent)