2 Augustine replied: The meaning of all this is, that the Hebrew prophets foretold nothing of Christ, and that, if they did, their predictions are of no use to us, and they themselves did not live suitably to the dignity of such prophecies. We must therefore prove the fact of the prophecies; and their use for the truth and steadfastness of our faith; and that the lives of the prophets were in harmony with their words. In this threefold discussion, it would take a long time under the first head to quote from all the books the passages in which Christ may be shown to have been predicted. Faustus' frivolity may be met effectually by the weight of one great authority. Although Faustus does not believe the prophets, he professes to believe the apostles. Above, as if to satisfy the doubts of some opponent, he declares that he assuredly believes the Apostle Paul. Let us then hear what Paul says of the prophets. His words are: "Paul, a servant of Jesus Christ, called to be an apostle, separated unto the gospel of God, which He had promised before by His prophets in the holy Scriptures, concerning His Son, who was made of the seed of David according to the flesh." What more does Faustus wish? Will he maintain that the apostle is speaking of some other prophets, and not of the Hebrew prophets? In any case, the gospel spoken of as promised was concerning the Son of God, who was made for Him of the seed of David according to the flesh: and to this gospel the apostle says that he was separated. So that the Manichæan heresy is opposed to faith in the gospel, which teaches that the Son of God was made of the seed of David according to the flesh. Besides, there are many passages where the apostle plainly testifies in behalf of the Hebrew prophets, with an authority by which the necks of these proud Manichæans are broken.
3. "I speak the truth in Christ," says the apostle, "I lie not, my conscience bearing me witness in the Holy Ghost, that I have great heaviness and continual sorrow of heart. For I could wish that myself were accursed from Christ, for my brethren, my kinsmen according to the flesh: who are Israelites; to whom pertains the adoption, and the glory, and the covenants, and the giving of the law, and the service and the promises; whose are the fathers, and of whom, as concerning the flesh, Christ came, who is over all, God blessed for ever." Here is the most abundant and express testimony and the most solemn commendation. The adoption here spoken of is evidently through the Son of God; as the apostle says to the Galatians: "In the fullness of time, God sent forth His Son, made of a woman, made under the law, that He might redeem them that were under the law, that we might receive the adoption of sons." And the glory spoken of is chiefly that of which he says in the same Epistle to the Romans: "What advantage has the Jew? Or what profit is there in circumcision? Much every way: chiefly, because unto them were committed the oracles of God." Can the Manichæans tell us of any oracles of God committed to the Jews besides those of the Hebrew prophets? And why are the covenants said to belong especially to the Israelites, but because not only was the Old Testament given to them, but also the New was prefigured in the Old? Our opponents often display much ignorant ferocity in attacking the dispensation of the law given to the Israelites, not understanding that God wishes us to be not under the law, but under grace. They are here answered by the apostle himself, who, in speaking of the advantages of the Jews, mentions this as one, that they had the giving of the law. If the law had been bad, the apostle would not have referred to it in praise of the Jews. And if Christ had not been preached by the law, the Lord Himself would not have said, "If you believe Moses, you would have believed me, for he wrote of me;" nor would He have borne the testimony He did after His resurrection, saying, "All things must needs be fulfilled that were written in the law of Moses, and in the Prophets, and in the Psalms, concerning me."
Source: Reply to Faustus the Manichaean (New Advent)