1 We have just heard out of the Gospel the words of the Lord which follow the former discourse. From these a discourse is due to your ears and minds, and it is not unseasonable today; for it is concerning the body of the Lord which He said that He gave to be eaten for eternal life. And He explained the mode of this bestowal and gift of His, in what manner He gave His flesh to eat, saying, “He that eats my flesh, and drinks my blood, dwells in me, and I in him.” The proof that a man has eaten and drank is this, if he abides and is abode in, if he dwells and is dwelt in, if he adheres so as not to be deserted.
This, then, He has taught us, and admonished us in mystical words that we may be in His body, in His members under Himself as head, eating His flesh, not abandoning our unity with Him. But most of those who were present, by not understanding Him, were offended; for in hearing these things, they thought only of flesh, that which themselves were. But the apostle says, and says what is true, “To be carnally-minded is death.” The Lord gives us His flesh to eat, and yet to understand it according to the flesh is death; while yet He says of His flesh, that therein is eternal life. Therefore we ought not to understand the flesh carnally. As in these words that follow:
Source: Tractates on the Gospel of John (New Advent)