John Calvin Commentary Numbers 16:48

"And he stood between the dead and the living; and the plague was stayed." — Numbers 16:48 (ASV)

And he stood between the living and the dead. If you understand that the living were everywhere mingled with the dead, you may conjecture that God's wrath did not fall upon one part of the camp in such a way as to destroy all that came in its path without exception, as had been the case in the other revolt, but that He selected those who had sinned most grievously.

But it is probable that Aaron went so far as to leave behind those who still remained uninjured and, in the very place where the destruction had occurred, encountered the wrath of God and arrested its course. Thus, both the fervor of his zeal could be better perceived, and his office of appeasing God was more fully confirmed by its actual success. For what more evident miracle could be required than when the slaughter—which had both begun to rage suddenly and then proceeded no less rapidly and continuously—was stopped by Aaron's arrival, exactly as if a hedge had been set up against it?

The efficacy of the priesthood in propitiating God is therefore clearly and briefly set before us. From this we are taught that though we are so close to the reprobate when they perish that their destruction might reach us, we will still be safe from all evil if only Christ intercedes for us.