Commentaria in Summam contra Gentiles, Liber IV

In the last place, St. Thomas answers the authority from which the heretics took the occasion of attacking the truth of this sacrament¹. And he says that from what has been said it is evident that what ecclesiastical tradition holds concerning the sacrament of the Altar contains nothing impossible to God, who can do all things.

Nor is it even against the tradition of the Church that the Lord says: The words that I have spoken are spirit and life. Because the meaning is not that His true flesh would not be delivered to the faithful to be eaten in this sacrament, but because it is received in a certain spiritual manner, beyond the custom of other carnal foods; and not carnally, as though to be torn apart in its proper appearance.

It should be noted that, according to the interpretation of these words set down here, the meaning is: The words that I have spoken to you about eating my flesh have a spiritual sense; because, namely, they are understood not as meaning that my flesh is to be eaten carnally, after the manner of other foods that are torn with the teeth, but that it is to be received in a spiritual manner. And understood in this way, they are life, that is, they bestow life.

St. Thomas also adds another sense, on John², according to the mind of Augustine, namely: — The words that I have spoken to you are to be referred to the Spirit joined to the flesh. Because, namely, the flesh of Christ, considered in itself, insofar as it is flesh, profits nothing; for it has no other effect than other flesh. But joined to the Word and to the Holy Spirit, it profits much, and bestows eternal life. And understood in this way, they are the life of the soul, that is, that which is expressed through them is the life of the soul, because the soul lives by a spiritual life through the Holy Spirit and the divinity.