15 If any truth about God or the Son of God is taught or predicted in the Sibyl or Sibyls, or in Orpheus, or in Hermes, if there ever was such a person, or in any other heathen poets, or theologians, or sages, or philosophers, it may be useful for the refutation of Pagan error, but cannot lead us to believe in these writers. For while they spoke, because they could not help it, of the God whom we worship, they either taught their fellow-countrymen to worship idols and demons, or allowed them to do so without daring to protest against it.
But our sacred writers, with the authority and assistance of God, were the means of establishing and preserving among their people a government under which heathen customs were condemned as sacrilege. If any among this people fell into idolatry or demon-worship, they were either punished by the laws, or met by the awful denunciations of the prophets. They worshipped one God, the maker of heaven and earth. They had rites; but these rites were prophetic, or symbolic of things to come, and were to cease on the appearance of the things signified.
The whole state was one great prophet, with its king and priest symbolically anointed which was discontinued, not by the wish of the Jews themselves, who were in ignorance through unbelief, but only on the coming of Him who was God, anointed with spiritual grace above His fellows, the holy of holies, the true King who should govern us, the true Priest who should offer Himself for us. In a word, the predictions of heathen ingenuity regarding Christ's coming are as different from sacred prophecy as the confession of devils from the proclamation of angels.
Source: Reply to Faustus the Manichaean (New Advent)