This is a harsh saying. On the contrary, it was in their hearts, and not in the saying, that the harshness lay. But out of the word of God the reprobate are thus accustomed to form stones to dash themselves upon, and when, by their hardened obstinacy, they rush against Christ, they complain that his saying is harsh, which ought rather to have softened them. For whoever shall submit with true humility [1] to the doctrine of Christ will find nothing in it harsh or disagreeable; but to unbelievers, who oppose themselves with obstinacy, it will be a hammer which breaketh the rocks in pieces, as the Prophet calls it, (Jeremiah 23:29.) But since the same hardness is natural to us all, if we judge of the doctrine of Christ according to our feelings, his words will be just so many strange and incredible [2] statements. All that remains for us, therefore, is, that every one commit himself to the guidance of the Spirit, that he may inscribe on our hearts what otherwise would never have even entered into our ears. Who can hear it? Here we see the awful wickedness of unbelief; for they who impiously and basely reject the doctrine of salvation, not satisfied with excusing themselves, have the hardihood to put the Son of God in their room as if he were guilty, and to declare that he is unworthy of being heard Thus, in the present day, Papists not only reject the Gospel in a daring manner, but likewise break out into horrid blasphemies, that it may not be thought that they have no good reason for opposing God. And, indeed, since they desire darkness, we need not wonder if Satan deceives them by strange monsters, where there is nothing but the open highway. [3] But that which they, through their rage and fury, cannot endure will not only be tolerable to modest and teachable persons, but will support and comfort them. Yet the reprobate, by their obstinate slanders, will do nothing more than bring down on themselves more dreadful condemnation.

Footnotes

1 - "En vraye humilite."

2 - "Estranges et incroyables."

3 - "La ou il n'y a que le beau plein chemin."

Many of his disciples - The word "disciple" means "learner." It was applied to the followers of Christ because they were taught by him. It does not imply, of necessity, that those to whom it was given were real Christians, but simply that they were under his teaching, and were professed learners in his school. See Matthew 17:16; Mark 2:18; John 9:28; Matthew 10:24. It is doubtless used in this sense here. It is, however, often applied to those who are real Christians.
This is an hard saying - The word "hard" here means "offensive, disagreeable" - that which they could not bear. Some have understood it to mean "difficult to be understood," but this meaning does not suit the connection. The doctrine which he delivered was opposed to their prejudices; it seemed to be absurd, and they therefore rejected it.
Saying - Rather doctrine or speech - Greek, λόγος logos. It does not refer to any particular part of the discourse, but includes the whole.
Who can hear it? - That is, who can hear it patiently - who can stay and listen to such doctrine or believe it. The effect of this is stated in John 6:66. The doctrines which Jesus taught that were so offensive appear to have been:
1. that he was superior to Moses.
2. that God would save all that he had chosen and those only.
3. that he said he was the bread that came from heaven.
4. that it was necessary to partake of that; that it was necessary that an atonement should be made, and that they should be saved by that.
These doctrines have always been among the most offensive that men have been called on to believe, and many, rather than trust in them, have chosen to draw back to perdition.

Many therefore of his disciples - So it appears that he had many more than the twelve, who constantly accompanied him.
This is a hard saying; who can hear it? - Who can digest such doctrine as this? It is intolerable: it is impracticable. There is a similar saving in Euripides, to the σκληρος λογος of the evangelist. Ποτερα θελεις σοι μαλθακα ψευδη λεγω, η σκληρ' αληθη, φραζε; Tell me whether thou wouldst that I should speak unto thee, a Soft Lie, or the Harsh Truth? The wicked word of a lying world is in general better received than the holy word of the God of truth!

(13) Many therefore of his disciples, when they had heard [this], said, This is an hard saying; who can hear it?
(13) The reason of man cannot comprehend the uniting of Christ and his members: therefore let it worship and revere that which is better than itself.

Many therefore of his disciples,.... Not of the twelve, nor of the seventy, but of the multitude of the disciples, who followed him from place to place, attended on his ministry, and might be baptized in his name; see John 4:1;
when they had heard this; that his flesh and blood were truly and really meat and drink, and that none had life in them, or should have eternal life, but such as eat and drink the same:
said, this is an hard saying; or it is to be objected to; so "an hard thing", the word here used in the Syriac version, and , "it is to me a hard thing", are phrases used to express an objection in the Talmudic writings, where they are often met with: or it is difficult to be understood and received; so , "an hard saying", or "an hard cause", is a cause difficult to be tried and determined, Exodus 18:26, and is used of that which seems incredible and absurd, and is surprising and unaccountable: so it is said (z), that
"it happened to a certain woman, that she came before R. Abika: she said to him, I have seen a spot; he said to her, perhaps there is a wound in thee; she answered him, yes, and it is healed; he replied, perhaps it may be opened, and the blood brought out; she answered him, yes; and he pronounced her clean. R. Abika saw his disciples look upon one another; and he said unto them, , "is this an hard saying with you?"''
is it a difficult thing with you? does it seem absurd to you? or are you surprised at it? anything difficult, or which seems irreconcilable, is so called: so the slaying the passover between the two evenings is called by Aben Ezra, in Exodus 12:6, , "an hard saying". In like sense the phrase is used here; and the allusion may be to food that is hard of digestion, since Christ had been speaking of himself under the metaphors of bread and meat. As some of the doctrines of Christ are comparable to milk, which is easy of digestion; others are like to strong meat, which belongs to those of full age, and cannot be digested by children, by babes in Christ, and much less be received, ate, and digested, with ease and pleasure, by carnal minds; who therefore say, as these Capernaites did,
who can hear it? this saying, or doctrine, concerning eating the flesh, and drinking the blood of Christ; or "him" Christ, who delivered this doctrine: such preaching, and such a preacher, are intolerable; there is no hearing, nor bearing them: hence we afterwards read, that these withdrew from the ministry of Christ, John 6:66.
(z) Misn. Nidda, c. 8, sect. 3.

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.

Many . . . of his disciples--His pretty constant followers, though an outer circle of them.
hard saying--not merely harsh, but insufferable, as the word often means in the Old Testament.
who can hear--submit to listen to it.

This is a hard saying. About eating and drinking his flesh and blood. They could not comprehend.

This is a hard saying - Hard to the children of the world, but sweet to the children of God. Scarce ever did our Lord speak more sublimely, even to the apostles in private. Who can hear - Endure it?