"Our Lord Himself, when He was speaking in praise of this same earth, said, “It is the Spirit that quickens, the flesh profits nothing.”...But when our Lord praised it, He was speaking of His own flesh, and He had said, “Except a man eat My flesh, he shall have no life in him.” (Jn 6:54) Some disciples of His, about seventy, were offended, and said, “This is an hard saying, who can hear it?” And they went back, and walked no more with Him. It seemed unto them hard that He said, “Except you eat the flesh of the Son of Man, you have no life in you:” they received it foolishly, they thought of it carnally, and imagined that the Lord would cut off parts from His body, and give unto them; and they said, “This is a hard saying.” It was they who were hard, not the saying; for unless they had been hard, and not meek, they would have said unto themselves, He says not this without reason, but there must be some latent mystery herein. They would have remained with Him, softened, not hard: and would have learned that from Him which they who remained, when the others departed, learned. For when twelve disciples had remained with Him, on their departure, these remaining followers suggested to Him, as if in grief for the death of the former, that they were offended by His words, and turned back. But He instructed them, and says unto them, “It is the Spirit that quickens, but the flesh profits nothing; the words that I have spoken unto you, they are spirit, and they are life.” (Jn 6:63) Understand spiritually what I have said; you are not to eat this body which you see; nor to drink that blood which they who will crucify Me shall pour forth. I have commended unto you a certain mystery; spiritually understood, it will quicken. Although it is needful that this be visibly celebrated, yet it must be spiritually understood."
~St. Augustine: Expositions on the Psalms, 99:8.
Communion of the Apostles, by Luca Signorelli.
Panel, 1512; Museo Diocesano, Cortona.