Whoso - shall swear by the altar - As an oath always supposes a person who witnesses it, and will punish perjury; therefore, whether they swore by the temple or the gold, (Matthew 23:16), or by the altar or the gift laid on it, (Matthew 23:18), the oath necessarily supposes the God of the temple, of the altar, and of the gifts, who witnessed the whole, and would, even in their exempt cases, punish the perjury.

Whosoever therefore shall swear by the altar,.... Not that Christ allowed of swearing by the altar, or by the temple, or by heaven, or by any creature, animate or inanimate; for such swearing is elsewhere disapproved of by him, and forbid, but if a man did swear by the altar, he ought to know, and consider that he not only
sweareth by it, but by all the gifts, and offerings that are brought, and laid upon it,
and by all things thereon; whatever gifts and sacrifices are offered upon it; which, by being put there, become holy, as the altar itself: so that he that swears by the altar, swears also by the gifts of the altar; and consequently, according to their own traditions, such oaths must be binding.

Whose therefore shall swear by the altar, &c.--See on Matthew 5:33-37.

He that sweareth by the altar, sweareth by it, and by all things thereon - Not only by the gift, but by the holy fire, and the sacrifice; and above all, by that God to whom they belong; inasmuch as every oath by a creature is an implicit appeal to God.