19 It may be well that Faustus, or at least that those who are charmed with Faustus' writings, should know that the doctrine of a single principle did not come to us from the Gentiles; for the belief in one true God, from whom every kind of nature is derived, is a part of the original truth retained among the Gentiles, notwithstanding their having fallen away to many false gods. For the Gentile philosophers had the knowledge of God, because, as the apostle says, "the invisible things of God, from the creation of the world, are clearly seen, being understood by the things that are made, even His eternal power and Godhead; so that they are without excuse."
But, as the apostle adds, "when they knew God, they glorified Him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened. Professing themselves to be wise, they became fools, and changed the glory of the incorruptible God into an image made like to corruptible man, and to birds, and four-footed beasts, and creeping things." These are the idols of the Gentiles, which they cannot explain except by referring to the creatures made by God; so that this very explanation of their idolatry, on which the more enlightened Gentiles were wont to pride themselves as a proof of their superiority, shows the truth of the following words of the apostle: "They worshipped and served the creature rather than the Creator, who is blessed forever." Where you differ from the Gentiles, you are in error; where you resemble them, you are worse than they.
You do not believe, as they do, in a single principle; and so you fall into the impiety of believing the substance of the one true God to be liable to subjugation and corruption. As regards the worship of a plurality of gods, the doctrine of lying devils has led the Gentiles to worship many idols, and you to worship many phantasms.
Source: Reply to Faustus the Manichaean (New Advent)