2 Augustine replied: After the long reply of last book, a short answer may suffice here. To one who has read that reply, it must seem insanity in Faustus to persist in denying that Christ was foretold by the Hebrew prophets, when the Hebrew nation was the only one in which the name Christ had a peculiar sacredness as applied to kings and priests; in which sense it continued to be applied till the coming of Him whom those kings and priests typified. Where did the Manichæan learn the name of Christ?
If from Manichæus, it is very strange that Africans, not to speak of others, should believe the Persian Manichæus, since Faustus finds fault with the Romans and Greeks, and other Gentiles, for believing the Hebrew prophets as belonging to another race. According to Faustus, the predictions of the Sibyl, or Orpheus, or any heathen poet, are more suitable for leading Gentiles to believe in Christ. He forgets that none of these are read in the churches, whereas the voice of the Hebrew prophets, sounding everywhere, draws swarms of people to Christianity. When it is so evident that men are everywhere led to Christ by the Hebrew prophets, it is great absurdity to say that those prophets are not suitable for the Gentiles.
Source: Reply to Faustus the Manichaean (New Advent)