Hebrews 6:16,17

For men verily swear by the greater By persons greater than themselves, whose vengeance they imprecate if they swear falsely; and particularly by Him who is infinitely greater than themselves; and an oath for confirmation To confirm what is promised or asserted; is to them an end of all strife Πασης αντιλογιας περας, usually puts an end to all contradiction. This shows that an oath taken in a religious manner, is lawful, even under the gospel: otherwise the apostle would never have mentioned it with so much honour, as a proper means to confirm the truth. Wherein In which business of confirming his promise; God, willing more abundantly Beyond what was absolutely necessary, and out of his superabundant love to and care for us; to show unto the heirs of promise To Abraham's spiritual seed, whose faith is counted for righteousness, and who partake of the blessings promised; the immutability of his counsel Of his purpose, which is accompanied with infinite wisdom; confirmed it Greek, εμεσιτευσεν, interposed, or came between the making of the promise and its accomplishment. The expression, says Macknight, “literally signifies, he mediatored it with an oath: he made an oath, the mediator, surety, or ratifier of his counsel.” This sense of the word merits attention, because it suggests a fine interpretation of Hebrews 9:15, where see the note. What amazing condescension was this of God! He, who is greatest of all, acts as if he were a middle person; as if, while he swears, he were less than himself, by whom he swears.