22 We have now only to compare the authority of Manichæus with that of the apostles. The genuineness of the writings is equally certain in both cases. But no one will compare Manichæus to the apostles, unless he ceases to be a follower of Christ, who sent the apostles. Who that did not misunderstand Christ's words ever found in them the doctrine of two natures opposed to one another, and having each its own principle? Again, the apostles, as becomes the disciples of truth, declare the birth and passion of Christ to have been real events; while Manichæus, who boasts that he leads into all truth, would lead us to a Christ whose very passion he declares to have been an illusion.
The apostles say that Christ was circumcised in the flesh which He took of the seed of Abraham; Manichæus says that God, in his own nature, was cut in pieces by the race of darkness. The apostles say that a sacrifice was offered for Christ as an infant in our nature, according to the institutions of the time; Manichæus, that a member, not of humanity, but of the divine substance itself, must be sacrificed to the whole host of demons by being introduced into the nature of the hostile race.
The apostles say that Christ, to set us an example, was baptized in the Jordan; Manichæus, that God immersed himself in the pollution of darkness, and that he will never wholly emerge, but that the part which cannot be purified will be condemned to eternal punishment. The apostles say that Christ, in our nature, was tempted by the chief of the demons; Manichæus, that part of God was taken captive by the race of demons. And in the temptation of Christ He resists the tempter; while in the captivity of God, the part taken captive cannot be restored to its origin even after victory.
To conclude, Manichæus, under the guise of an improvement, preaches another gospel, which is the doctrine of devils; and the apostles, after the doctrine of Christ, enjoin that whoever preaches another gospel shall be accursed.
Source: Reply to Faustus the Manichaean (New Advent)