4 But because the Manichæans preach another Christ, and not Him whom the apostles preached, but a false Christ of their own false contrivance, in imitation of whose falsehood they themselves speak lies, though they may perhaps be believed when they are not ashamed to profess to be the followers of a deceiver, that has befallen them which the apostle asserts of the unbelieving Jews: "When Moses is read, a veil is upon their heart." Neither will this veil which keeps them from understanding Moses be taken away from them till they turn to Christ; not a Christ of their own making, but the Christ of the Hebrew prophets.
For, as the apostle says, "When you shall turn to the Lord, the veil shall be taken away." We cannot wonder that they do not believe in the Christ who rose from the dead, and who said, "All things must needs be fulfilled which were written in the law of Moses, and in the prophets, and in the Psalms, concerning me;" for this Christ has Himself told us what Abraham said to a hard-hearted rich man when he was in torment in hell, and asked Abraham to send some one to his brothers to teach them, that they might not come too into that place of torment.
Abraham's reply was: "They have Moses and the prophets, let them hear them." And when the rich man said that they would not believe unless some one rose from the dead, he received this most truthful answer: "If they hear not Moses and the prophets, neither will they believe even though one rose from the dead." Wherefore, the Manichæans will not hear Moses and the prophets, and so they do not believe Christ, though He rose from the dead. Indeed, they do not even believe that Christ rose from the dead. For how can they believe that He rose, when they do not believe that He died? For, again, how can they believe that He died, when they deny that He had a mortal body?
Source: Reply to Faustus the Manichaean (New Advent)