6 If you will not eat flesh why should you not slay animals in sacrifice to your God, in order that their souls, which you hold to be not only human, but so divine as to be members of God Himself, may be released from the confinement of flesh, and be saved from returning by the efficacy of your prayers? Perhaps, however, your stomach gives more effectual aid than your intellect, and that part of divinity which has had the advantage of passing through your bowels is more likely to be saved than that which has only the benefit of your prayers.
Your objection to eating flesh will be that you cannot eat animals alive, and so the operation of your stomach will not avail for the liberation of their souls. Happy vegetables, that, torn up with the hand, cut with knives, tortured in fire, ground by teeth, yet reach alive the altars of your intestines! Unhappy sheep and oxen, that are not so tenacious of life, and therefore are refused entrance into your bodies! Such is the absurdity of your notions. And you persist in making out an opposition in us to the Old Testament, because we consider no flesh unclean: according to the opinion of the apostle, "To the pure all things are pure;" and according to the saying of our Lord Himself, "Not that which goes into your mouth defiles you, but that which comes out." This was not said to the crowd only, as your Adimantus, whom Faustus, in his attack on the Old Testament, praises as second only to Manichæus, wishes us to understand; but when retired from the crowd, the Lord repeated this still more plainly and pointedly to His disciples.
Adimantus quotes this saying of our Lord in opposition to the Old Testament, where the people are prohibited from eating some animals which are pronounced unclean; and doubtless he was afraid that he should be asked why, since he quotes a passage from the Gospel about man not being defiled by what enters into his mouth and passes into his belly, and out into the draft, he yet considers not some only, but all flesh unclean, and abstains from eating it. It is in order to escape from this strait, when the plain truth is too much for his error, that he makes the Lord say this to the crowd; as if the Lord were in the habit of speaking the truth only in small companies, while He blurted out falsehoods in public.
To speak of the Lord in this way is blasphemy. And all who read the passage can see that the Lord said the same thing more plainly to His disciples in private. Since Faustus praises Adimantus so much at the beginning of this book of his, placing him next to Manichæus, let him say in a word whether it is true or false that a man is not defiled by what enters into his mouth. If it is false, why does this great teacher Adimantus quote it against the Old Testament? If it is true, why, in spite of this, do you believe that eating any flesh will defile you?
It is true, if you choose this explanation, that the apostle does not say that all things are pure to heretics, but, "to the pure all things are pure." The apostle also goes on to explain why all things are not pure to heretics: "To the impure and unbelieving nothing is pure, but both their mind and conscience are defiled." So to the Manichæans there is absolutely nothing pure; for they hold that the very substance or nature of God not only may be, but has actually been defiled, and so defiled that it can never be wholly restored and purified.
What do they mean when they call animals unclean, and refrain from eating them, when it is impossible for them to think anything, whether food or whatever it may be, clean? According to them, vegetables too, fruits, all kinds of crops, the earth and sky, are defiled by mixture with the race of darkness. Why do they not act up to their opinions about other things as well as about animals? Why do they not abstain altogether, and starve themselves to death, instead of persisting in their blasphemies? If they will not repent and reform, this is evidently the best thing that they could do.
Source: Reply to Faustus the Manichaean (New Advent)