2 “Many therefore,” not of His enemies, but “of His disciples, when they had heard this, said, This is a hard saying; who can hear it?” If His disciples accounted this saying hard, what must His enemies have thought? And yet so it behooved that to be said which should not be understood by all. The secret of God ought to make men eagerly attentive, not hostile. But these men quickly departed from Him, while the Lord said such things: they did not believe Him to be saying something great, and covering some grace by these words; they understood just according to their wishes, and in the manner of men, that Jesus was able, or was determined upon this, namely, to distribute the flesh with which the Word was clothed, piecemeal, as it were, to those that believe in Him. “This,” say they, “is a hard saying; who can hear it?”
Source: Tractates on the Gospel of John (New Advent)