Albert Barnes Commentary Matthew 21:44

"And he that falleth on this stone shall be broken to pieces: but on whomsoever it shall fall, it will scatter him as dust." — Matthew 21:44 (ASV)

Whosoever shall fall, etc. There is an allusion here, undoubtedly, 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. Whoever falls on it will be broken; whoever runs against it—a cornerstone, standing out from the other parts of the foundation—will be injured, or broken in his limbs or body. Whoever is offended by my being the foundation, or who opposes me, will, by that act, injure himself, making himself miserable by doing so, even if there were nothing further. But there is something further.

On whomsoever it shall fall, it will grind him to powder. That is, in the original, it will reduce him to dust, so that it may be scattered by the winds.

There is an allusion here, undoubtedly, 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 Savior speaks of the falling of the stone on his enemies. Those who oppose him, reject him, and continue impenitent, will be crushed by him in the day of judgment and perish forever.