John Calvin on Hebrews 6:13-15

13. For when God made a promise to Abraham, etc. His object was to prove, that the grace of God is offered to us in vain, except we receive the promise by faith, and constantly cherish it in the bosom of our heart. And he proves it by this argument, that when God promised a countless offspring to Abraham, it seemed a thing incredible; Sarah had been through life barren; both had reached a sterile old age, when they were nearer the grave than to a conjugal bed; there was no vigor to beget children, when Sarah’s womb, which had been barren through the prime of life, was now become dead. Who could believe that a nation would proceed from them, equaling the stars in number, and like the sand of the sea? It was, indeed, contrary to all reason. Yet Abraham looked for this and feared no disappointment, because he relied on the Word of God. It is said, that having “patiently endured” or rather waited, “he obtained the promise,” that is, of a numerous posterity, the particular thing previously referred to. After having waited for twenty-five years, (see Genesis 12:1-4, and Genesis 17:1-16,) a son was given him; and this beginning of the fulfilled promise was a pledge of its full accomplishment. This case is brought forward as an example of waiting faith. — Ed. We must, then, notice the circumstance as to time, that the Apostle’s reasoning may appear evident; and what he subjoins refers to this — that he was made partaker of this blessing, but that it was after he had waited for what no one could have thought would ever come to pass. In this way ought glory to be given to God; we must quietly hope for what he does not as yet show to our senses, but hides from us and for a long time defers, in order that our patience may be exercised.

Why God did swear by himself we shall presently see. The manner of swearing, Except blessing I will bless thee, we have explained what it means in the third chapter: God’s name is not here expressed, but must be understood, for except he performs what he promises, he testifies that he is not to he counted true and faithful.

Hebrews Chapter 6:16-20

16. For men verily swear by the greater: and an oath for confirmation is to them an end of all strife.

16. Nam homines quidem per eum jurant qui major est, et omnis ipsis controversiae finis est jusjurandum in confirmationem.

17. Wherein God, willing more abundantly to shew unto the heirs of promise the immutability of his counsel, confirmed it by an oath:

17. In quo Deus volens uberius ostendere haeridibus promissionis immutabilem consilii sui firmitudinem, interposuit jusjurandum;

18. That by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us:

18. Ut per duas res immutabiles, in quibus impossibile sit Deum mentiri, validam consolationem habeamus nos qui confugimus ad obtinendam propositam spem;

19. Which hope we have as an anchor of the soul, both sure and steadfast, and which entereth into that within the veil;

19. Quam velut anchoram habemus animae tutam et firmam, et quae ingreditur ad ea quae intro velum sunt;.

20. Whither the forerunner is for us entered, even Jesus, made an high priest for ever after the order of Melchisedec.

20. Quo praecursor noster ingressus est Iesus, secondum ordinem Melchisedec factus in aeternum pontifex.