6 I am aware that instead of boldly pronouncing these passages spurious, you make out that these things were required of the Jews till the coming of Jesus; and that now that He has come, according, as you say, to the predictions of this Old Testament, He Himself teaches what we should receive, and what we should set aside as obsolete. Whether the prophets predicted the coming of Jesus we shall see presently. Meanwhile, I need say no more than that if Jesus, after being predicted in the Old Testament, now subjects it to this sweeping criticism, and teaches us to receive a few things and to throw over many things, in the same way the Paraclete who is promised in the New Testament teaches us what part of it to receive, and what to reject; as Jesus Himself says in the Gospel, when promising the Paraclete, "He shall guide you into all truth, and shall teach you all things, and bring all things to your remembrance." So then, with the help of the Paraclete, we may take the same liberties with the New Testament as Jesus enables you to take with the Old, unless you suppose that the Testament of the Son is of greater value than that of the Father, if it is really the Father's; so that while many parts of the one are to be condemned, the other must be exempted from all disapproval; and that, too, when we know, as I said before, that it was not written by Christ or by His apostles.
Source: Reply to Faustus the Manichaean (New Advent)