As Abraham was the first who was called when he was mingled with idolaters, the prophet begins with him. He, however, afterwards declares that the covenant was also confirmed in the hand of his son and his son's son. God then deposited his covenant with Abraham and by solemn oath engaged to be the God of Abraham's seed. To give greater assurance of the truth of his promise, he was graciously pleased to renew it with Isaac and Jacob. The effect of extending it in this way is that his faithfulness takes deeper hold on the hearts of people. Also, his grace, when it is thus testified to on frequent recurring occasions, becomes better known and more illustrious among men. Accordingly, it is here declared by gradation how steadfast and immoveable this covenant is; for what is affirmed concerning each of the patriarchs belongs equally to them all.
It is said that God swore to Isaac. But had he not sworn to Abraham before? Undoubtedly he had. It is also said that it was established to Jacob for a law, and for an everlasting covenant. Does this mean that the covenant was previously only temporal and transitory, and that then it had changed its nature? Such an idea is altogether at variance with the meaning of the sacred writer. By these different forms of expression he asserts that the covenant was fully and perfectly confirmed, so that, if perhaps the calling was obscure in one man, it might be more evident, by God's having transmitted the testimony of it to posterity; for by this means the truth of it was the better manifested. Here again we must remember that God with great kindness considers our weakness when, both by his oath, and by frequently repeating his word, he ratifies what he has once promised to us. Our ingratitude then appears the fouler in disbelieving him when he not only speaks but also swears.