Jerome

Again, if one swore by the altar, none held him guilty of perjury; but if he swore by the gift or the victims or the other things which are offered to God upon the altar, this they exacted most rigorously. And all this they did not out of fear of God, but out of covetousness. Thus the Lord charges them with both folly and fraud, inasmuch as the altar is much greater than the victims which are sanctified by the altar.

Catena Aurea by Aquinas ↗

Thomas Aquinas

Then he sets forth the second part of the tradition: and whosoever shall swear by the altar, it is nothing; but whosoever shall swear by the gift that is upon it, is a debtor.

Commentary on Matthew ↗