Hebrews 6:17

17.God, willing, etc. See how kindly God as a gracious Father accommodates himself to our slowness to believe; as he sees that we rest not on his simple word, that he might more fully impress it on our hearts he adds an oath. Hence also it appears how much it concerns us to know that there is such a certainty respecting his goodwill towards us, that there is no longer any occasion for wavering or for trembling. For when God forbids his name to be taken in vain or on a slight occasion, and denounces the severest vengeance on all who rashly abuse it, when he commands reverence to be rendered to his majesty, he thus teaches us that he holds his name in the highest esteem and honor. The certainty of salvation is then a necessary thing; for he who forbids to swear without reason has been pleased to swear for the sake of rendering it certain. And we may hence also conclude what great account he makes of our salvation; for in order to secure it, he not only pardons our unbelief, but giving up as it were his own right, and yielding to us far more than what we could claim, he kindly provides a remedy for it.

Unto the heirs of promise, etc. He seems especially to point out the Jews; for though the heirship came at length to the Gentiles, yet the former were the first lawful heirs, and the latter, being aliens, were made the second heirs, and that beyond the right of nature. So Peter, addressing the Jews in his first sermon, says,

“To you and to your children is the promise made, and to those who are afar of, whom the Lord shall call.” (Acts 2:39.)

He left indeed a place for adventitious heirs, but he sets the Jews in the first rank, according to what he also says in the third chapter, “Ye are the children of the fathers and of the covenant,” etc. (Acts 3:25.) So also in this place the Apostle, in order to make the Jews more ready to receive the covenant, shows that it was for their sakes chiefly it was confirmed by an oath. At the same time this declaration belongs at this day to us also, for we have entered into the place quitted by them through unbelief

Observe that what is testified to us in the Gospel is called the counsel of God, that no one may doubt but that this truth proceeds from the very inmost thoughts of God. Believers ought therefore to be fully persuaded that whenever they hear the voice of the Gospel, the secret counsel of God, which lay hid in him, is proclaimed to them, and that hence is made known to them what he has decreed respecting our salvation before the creation of the world.