11 Believing and teaching such monstrosities, and living accordingly, you yet have the boldness to say that you obey the precepts of the gospel, and to decry the Catholic Church, which includes many weak as well as strong, both of whom the Lord blesses, because both according to their measure obey the precepts of the gospel and hope in its promises. The blindness of hostility makes you see only the tares in our harvest: for you might easily see wheat too, if you were willing that there should be any. But among you, those who are pretended Manichæans are wicked, and those who are really Manichæans are silly. For where the faith itself is false, he who hypocritically professes it acts deceitfully, while he who truly believes is deceived. Such a faith cannot produce a good life, for every man's life is good or bad according as his heart is engaged. If your affections were set upon spiritual and intellectual good, instead of material forms, you would not pay homage to the material sun as a divine substance, and as the light of wisdom, which every one knows you do, though I now only mention it in passing.
Source: Reply to Faustus the Manichaean (New Advent)