Augustine of Hippo
Catena Aurea · Johannesevangelium 6
Many therefore of his disciples, when they had heard this, said, This is an hard saying; who can hear it? When Jesus knew in himself that his disciples murmured at it, he said unto them, Doth this offend you? What and if ye shall see the Son of man ascend up where he was before? It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life. But there are some of you that believe not. For Jesus knew from the beginning who they were that believed not, and who should betray him. And he said, Therefore said I unto you, that no man can come unto me, except it were given unto him of my Father. From that time many of his disciples went back, and walked no more with him. Then said Jesus unto the twelve, Will ye also go away? Then Simon Peter answered him, Lord, to whom shall we go? thou hast the words of eternal life. And we believe and are sure that thou art that Christ, the Son of the living God. Jesus answered them, Have not I chosen you twelve, and one of you is a devil? He spake of Judas Iscariot the son of Simon: for he it was that should betray him, being one of the twelve.
(Tr. xxvii) If then thou understandest them spiritually, they are life and spirit to thee: if carnally, even then they are life and spirit, but not to thee. Our Lord declares that in eating His body, and drinking His blood, we dwell in Him, and He in us. But what has the power to affect this, except love? The love of God is shed abroad in our hearts by the Holy Spirit, which is given to us. (Rom. 5:5)