John 6:64

As it is not the bread or flesh that a man eateth for the sustenance of his animal or natural life, that doth the main work, but the soul of a man within him, which putteth forth its virtues and powers in causing the digestion, concoction, and alteration of it, without which it nourisheth not the body; so the flesh of Christ eaten carnally can be of no profit for the nourishment of the soul: nor can the flesh of Christ considered alone, or by any virtue in it, profit; it only profiteth by virtue of the Divine nature, which being personally united to the human nature, addeth all the virtue and merit to the sufferings and actions of the human nature; so as the human nature of Christ hath all its quickening virtue from the Divine nature. It is not therefore the carnal eating of my flesh that I intended, that is a very gross conception of yours; nor can any such thing as that do you good: but the words that I speak to you, they are spiritual, and such by the belief of which you may obtain a spiritual and eternal life; for by believing those words, and obeying them, you shall come to believe in me, which is that eating my flesh and drinking my blood which I intended, not any corporeal or carnal eating.

The flesh profiteth nothing. Dead flesh, separated from the spirit, in the gross manner they supposed they were to eat his flesh, would profit nothing. Neither doth man’s flesh, that is to say, man’s natural and carnal apprehension, (which refuses to be subject to the spirit, and words of Christ) profit any thing. But it would be the height of blasphemy, to say the living flesh of Christ (which we receive in the blessed sacrament, with his spirit, that is, with his soul and divinity) profiteth nothing. For if Christ’s flesh had profited us nothing, he would never have taken flesh for us, nor died in the flesh for us. — Are spirit and life. By proposing to you a heavenly sacrament, in which you shall receive, in a wonderful manner, spirit, grace and life. These words sufficiently correct the gross and carnal imagination of these Capharnaites, that he meant to give them his body and blood to eat in a visible and bloody manner, as flesh, says St. Augustine, is sold in the market, and in the shambles;[3] but they do not imply a figurative or metaphorical presence only. The manner of Christ’s presence is spiritual and under the outward appearances of bread and wine; but yet he is there truly and really present, by a change of the substance of bread and wine into the substance of his body and blood, which truly and really become our spiritual food, and are truly and really received in the holy sacrament. — The flesh[4] of itself profiteth nothing, not even the flesh of our Saviour Christ, were it not united to the divine person of Christ. But we must take care how we understand these words spoken by our Saviour: for it is certain, says St. Augustine, that the word made flesh, is the cause of all our happiness. (Witham) — When I promise you life if you eat my flesh, I do not wish you to understand this of that gross and carnal manner, of cutting my members in pieces: such ideas are far from my mind: the flesh profiteth nothing. In the Scriptures, the word flesh is often put for the carnal manner of understanding any thing. If you wish to enter into the spirit of my words, raise your hearts to a more elevated and spiritual way of understanding them. (Calmet) — The reader may consult Des Mahis, p. 165, a convert from Protestantism, and who has proved the Catholic doctrine on the Eucharist in the most satisfactory manner, from the written word. Where he shows that Jesus Christ, speaking of his own body, never says the flesh, but my flesh: the former mode of expression is used to signify, as we have observed above, a carnal manner of understanding any thing.

[3.] He gives them an intimation of his knowledge of them, and that he had expected no better from them, though they called themselves his disciples, v. 64, 65. Now was fulfilled that of the prophet, speaking of Christ and his doctrine (Isa 53 1), Who hath believed our report? and to whom is the arm of the Lord revealed? Both these Christ here takes notice of.

Verses 60-65 The human nature of Christ had not before been in heaven, but being God and man, that wondrous Person was truly said to have come down from heaven. The Messiah's kingdom was not of this world; and they were to understand by faith, what he had said of a spiritual living upon him, and his fulness. As without the soul of man the flesh is of no value, so without the quickening Spirit of God all forms of religion are dead and worthless. He who made this provision for our souls, alone can teach us these things, and draw us unto Christ, that we may live by faith in him. Let us apply to Christ, thankful that it is declared that every one who is willing to come unto him shall be made welcome.