And he who shall fall on this stone. Christ confirms more fully the former statement, that he suffers no loss or diminution when he is rejected by the wicked, because, though their obstinacy were like a stone or like iron, yet by his own hardness he will break them, and therefore he will be the more highly glorified in their destruction. He perceived in the Jews an astonishing obstinacy, and therefore it was necessary that this kind of punishment should be described to them in an alarming manner, that they might not flatter themselves, while they thus dashed against him. This doctrine partly instructs us to give ourselves up gently, with a mild and tractable heart, to the dominion of Christ, and partly fortifies us against the obstinacy and furious attacks of the wicked, for whom there awaits a dreadful end. Those persons are said to fall upon Christ, who rush forward to destroy him; not that they occupy a more elevated position than he does, but because their madness carries them so far, that they endeavor to attack Christ as if he were below them. But Christ tells them that all that they will gain by it is, that by the very conflict they will be broken. But when they have thus proudly exalted themselves, he tells them that another thing will happen, which is, that they will be bruised under the stone, against which they so insolently dashed themselves.

Whosoever shall fall - There is a reference here, doubtless, to Isaiah 8:14-15. Having made an allusion to himself "as a stone," or a rock Matthew 21:42, he proceeds to state the consequences of coming in contact with it. He that falls upon it shall be broken; he that "runs against it" - a cornerstone, standing out from the other parts of the foundation shall be injured, or broken in his limbs or body. He that is offended with my being the foundation, or that opposes me, shall by the act injure himself, or make himself miserable "by so doing," even were there nothing further. But there is something further.
On whomsoever it shall fall, it will grind him to powder - That is, in the original, will reduce him to dust, so that it may be scattered by the winds. There is an allusion here, doubtless, to the custom of stoning as a punishment among the Jews. A scaffold was erected twice the height of the man to be stoned. Standing on its edge, he was violently struck off by one of the witnesses: if he died by the blow and the fall, nothing further was done; if not, a heavy stone was thrown down on him, which at once killed him. So the Saviour speaks of the "falling" of the stone on his enemies. They who oppose him, who reject him, and who continue impenitent, shall be crushed by him in the day of judgment, and perish forever.

The 44th verse should certainly come before Matthew 21:43, otherwise the narration is not consecutive.
Matthew 21:42. The stone which the builders rejected, is become the head of the corner, etc. Matthew 21:44. Whosoever shall fall on this stone shall be broken, etc. This is an allusion to the punishment of stoning among the Jews. The place of stoning was twice as high as a man; while standing on this, one of the witnesses struck the culprit on the loins, so that he fell over this scaffold; if he died by the stroke and fall, well; if not, the other witness threw a stone upon his heart, and despatched him. That stone thrown on the culprit was, in some cases, as much as two men could lift up. Tract Sanhed. and Bab. Gemara, and Lightfoot. See also the note on John 8:7 (note).
He, whether Jew or Gentile, who shall not believe in the Son of God, shall suffer grievously in consequence; but on whomsoever the stone (Jesus Christ) falls in the way of judgment, he shall be ground to powder, λικμησει αυτον - it shall make him so small as to render him capable of being dispersed as chaff by the wind. This seems to allude, not only to the dreadful crushing of the Jewish state by the Romans, but also to that general dispersion of the Jews through all the nations of the world, which continues to the present day. This whole verse is wanting in the Codex Bezae, one other, five copies of the Itala, and Origen; but it is found in the parallel place, Luke 20:18, and seems to have been quoted from Isaiah 8:14, Isaiah 8:15. He shall be for a Stone of Stumbling, and for a Rock of Offence to both the houses of Israel - and many among them shall Stumble and Fall, and be Broken.

And whosoever shall fall on this stone shall be broken: but on whomsoever it shall fall, it will (b) grind him to powder.
(b) As chaff used to be scattered with the wind, for he uses a word which properly signifies separating the chaff from the corn with winnowing, and to scatter it abroad.

And whosoever shall fall on this stone,.... This is not to be understood of believing in Christ, or of a soul's casting itself on Christ, the foundation stone; relying on him, and building all its hopes of happiness and salvation on him; which is attended with contrition and brokenness of heart, or repentance unto life, which needed not to be repented of nor of a believer's offending Christ by evil works, whereby his conscience is wounded, his soul is grieved, and his faith shaken; and though he is hereby in great danger, he shall not be utterly destroyed, but being recovered by repentance, shall be preserved unto salvation; but of such to whom Christ is a stone of stumbling, and a rock of offence: for as he is the foundation and corner stone to some, and is set for the rising of them, and to whom he is precious; so he is a stone set for the fall of others, and at which they stumble and fall, and fall upon it: and such are they who are offended at Christ's state of humiliation on earth; at the manner of his birth, the meanness of his parentage, and education; the despicable figure he made in his person, disciples, and audience; and at his sufferings and death: and these "shall be broken": as a man that stumbles at a stone, and falls upon it, breaks his head or his bones, at least bruises himself, does not hurt the stone, but the stone hurts him; so all such as are offended at Christ, injure their own souls, being filled with prejudices against him, and contempt and disbelief of him, which if grace prevents not will issue in their everlasting destruction: but whilst there is life, the means of grace continue, the kingdom of God is not taken away; there is hope that such may be recovered from their impenitence and unbelief: "but on whomsoever it shall fall, it will grind him to powder". Just as if a millstone, or any stone of such like weight and bulk, was to fall upon an earthen vessel; or, as the stone cut out of the mountain without hands, by which the Messiah and his kingdom, are designed, brake in pieces the image in Nebuchadnezzar's dream, so that it became like the chaff of the summer threshing floor. As the former part of this verse expresses the sin of unbelievers, and the danger they are exposed unto by it, this sets forth their punishment; and has respect both to the vengeance of Christ, on the Jewish nation, at their destruction, which would fall heavy from him in his state of exaltation, for their evil treatment of him in his state of humiliation; and to his severe wrath, which will be executed at the day of judgment on all unbelievers, impenitent Christless sinners, who have both offended him, and been offended at him; when their destruction will be inevitable, their salvation irretrievable, and their souls irrecoverably lost, and ruined. Some have thought, that there is an allusion in these words to the manner of stoning among the Jews, which was this (e):
"the place of stoning was two men's heights; one of the witnesses struck him on his loins, to throw him down from thence, to the ground: if he died, it was well; if not, they took a stone, which lay there, and was as much as two men could carry, and cast it, with all their might, upon his breast: if he died, it was well; if not, he was stoned by all Israel.
Maimonides observes (f), that "stoning, or throwing down from the high place, was that he might fall upon the stone, or that the stone might fall upon him; and which of them either it was, the pain was the same.
(e) Misu. Sanhedrin, c. 6. sect. 4. T. Bab. Sanhedrin, fol. 45. 1, 2. Maimon. Hilch. Sanhedrin, c. 15. sect 1. Moses Kotsensis Mitzvot Tora pr. Affirm. 99. (f) In Misn. Sanhedrin, c. 6. sect. 4.

And whosoever shall fall on this stone shall be broken: but on whomsoever it shall fall, it will grind him to powder--The Kingdom of God is here a Temple, in the erection of which a certain stone, rejected as unsuitable by the spiritual builders, is, by the great Lord of the House, made the keystone of the whole. On that Stone the builders were now "falling" and being "broken" (Isaiah 8:15). They were sustaining great spiritual hurt; but soon that Stone should "fall upon them" and "grind them to powder" (Daniel 2:34-35; Zac 12:2) --in their corporate capacity, in the tremendous destruction of Jerusalem, but personally, as unbelievers, in a more awful sense still.

Whoever shall fall on this stone shall be broken. Two fates are named for opposers in this verse; those who fall on the stone shall be broken; those on whom the stone shall fall shall be ground to powder. While the principle is general, the special application is to the Jewish opposers. Their falling upon the Stone (Christ) was the ruin of their nation. When the Stone fell upon them, in the judgment he had predicted because they rejected him, they were ground to powder in the awful desolation that occurred about thirty-seven years later.

Whosoever shall fall on this stone shall be broken - Stumblers at Christ shall even then receive much hurt. He is said to fall on this stone, who hears the Gospel and does not believe. But on whomsoever it shall fall - In vengeance, it will utterly destroy him. It will fall on every unbeliever, when Christ cometh in the clouds of heaven. Luke 20:18.