Hebrews 6:16

16.For men, etc. It is an argument from the less to the greater; if credit is given to man, who is by nature false, when he swears, and for this reason, because he confirms what he says by God’s name, how much more credit is due to God, who is eternal truth, when he swears by himself?

Now he mentions several things to commend this declaration; and first he says that men swear by the greater; by which he means that they who are wanting in due authority borrow it from another. He adds that there is so much reverence in an oath that it suffices for confirmation, and puts an end to all disputes where the testimonies of men and other proofs are wanting. Then is not he a sufficient witness for himself whom all appeal to as a witness? Is he not to obtain credit for what he says, who, by his authority, removes all doubts among others? If God’s name, pronounced by man’s tongue, possesses so much superiority, how much more weight ought it to have, when God himself swears by his own name? Thus much as to the main point.

But here in passing, two things are to be noticed, — that we are to swear by God’s name when necessity requires, and that Christians are allowed to make an oath, because it is a lawful remedy for removing contentions. God in express words bids us to swear by his name; if other names are blended with it, the oath is profaned. For this there are especially three reasons: when there is no way of bringing the truth to light, it is not right, for the sake of verifying it, to have recourse to any but to God, who is himself eternal truth; and then, since he alone knows the heart, his own office is taken from him, when in things hidden, of which men can form no opinion, we appeal to any other judge; and thirdly, because in swearing we not only appeal to him as a witness, but also call upon him as an avenger of perjury in case we speak falsely. It is no wonder, then, that he is so greatly displeased with those who swear by another name, for his own honor is thus disparaged. And that there are different forms often used in Scripture, makes nothing against this truth; for they did not swear by heaven or earth, as though they ascribed any divine power to them, or attributed to them the least portion of divinity, but by this indirect protestation, so to speak, they had a regard to the one true God. There are indeed various kinds of protestations; but the chief one is, when we refer to God as a judge and directly appeal to his judgment­seat; another is, when we name things especially dear to us as our life, or our head, or anything of this kind; and the third is, when we call creatures as witnesses before God. But in all these ways we swear properly by no other than by God. hence they betray their impiety no less than their ignorance, who contend that it is lawful to connect dead saints with God so as to attribute to them the right of punishing.

Further, this passage teaches us, as it has been said, that an oath may be lawfully used by Christians; and this ought to be particularly observed, on account of fanatical men who are disposed to abrogate the practice of solemn swearing which God has prescribed in his Law. For certainly the Apostle speaks here of the custom of swearing as of a holy practice, and approved by God. Moreover, he does not say of it as having been formerly in use, but as of a thing still practiced. Let it then be employed as a help to find out the truth when other proofs are wanting.