Jamieson, Fausset and Brown on Matthew 23:16

16. Woe unto you, ye blind guides--Striking expression this of the ruinous effects of erroneous teaching. Our Lord, here and in some following verses, condemns the subtle distinctions they made as to the sanctity of oaths--distinctions invented only to promote their own avaricious purposes.

which say, Whosoever shall swear by the temple, it is nothing--He has incurred no debt.

but whosoever shall swear by the gold of the temple--meaning not the gold that adorned the temple itself, but the Corban, set apart for sacred uses (see on Mt 15:5).

he is a debtor!--that is, it is no longer his own, even though the necessities of the parent might require it. We know who the successors of these men are.

but whosoever sweareth by the gift that is upon it, he is guilty--It should have been rendered, "he is a debtor," as in Mt 23:16.