Barnes New Testament Notes

Verse 13. For when God made promise to Abraham. That he would bless him, and multiply his seed as the stars of heaven, Ge 22:16,17. The object of introducing this example here is to encourage those to whom the apostle was writing to persevere in the Christian life. This he does by showing that God had given the highest possible assurance of his purpose to bless his people by an oath. Reference is made to Abraham in this argument probably, for two reasons.

(1.) To show the nature of the evidence which Christians have that they will be saved, or the ground of encouragement -- being the same as that made to Abraham, and depending, as in his case, on the promise of God; and

(2.) because the example of Abraham was just in point. He had persevered. He had relied firmly and solely on the promise of God. He did this when appearances were much against the fulfilment of the promise, and he thus showed the advantage of perseverance and fidelity in the cause of God.

Because he could swear by no greater. There is no being greater than God. In taking an oath among men it is always implied that the appeal is to one of superior power, who is able to punish for its infraction. But this could not occur in the case of God himself. There was no greater being than himself, and the oath, therefore, was by his own existence.

He sware by himself. Ge 22:16: "By myself have I sworn." Comp. Isa 45:23. In an oath of this kind God pledges his veracity; declares that the event shall be as certain as his existence; and secures it by all the perfections of his nature. The usual form of the oath is, "As I live, saith the Lord." See Nu 14:21,28; Eze 33:11.