That's not entirely what the Bible says. It says that God made promises with Abraham and through Isaac that He intended to keep forever.
God saves and sustains the seed of Isaac through covenant promises by establishing an everlasting, unilateral guarantee rooted in His own faithfulness rather than human merit or mere abstract faith. This is demonstrated through divine election, where God chose Isaac over Ishmael before birth to fulfill the covenant, proving that salvation depends on sovereign grace and God's initiative, not human works.
1. Unconditional Assurance
Genesis 17:7 — "And I will establish my covenant between me and you and your offspring after you throughout their generations for an everlasting covenant, to be God to you and to your offspring after you."
The Hebrew word for "establish" is qûm (קוּם, #06965) in the Hiphil stem. As the Free Bible Commentary notes: "This VERB in the Hiphil stem is used with oaths to assure their fulfillment (cf. Gen. 6:18; 17:19; Exod. 6:4; Lev. 26:9; Ezek. 16:62). YHWH is committing Himself to the completion of His promises." The REV Bible Commentary adds: "This covenant with Abraham is something God initiates, something He maintains, and something He brings to fulfillment" — resting entirely on the Lord's burden, independent of human performance.
Genesis 17:19 — "But God said, 'No. Sarah your wife will bear you a son, and you shall call his name Isaac. I will establish my covenant with him as an everlasting covenant for his descendants after him.'"
The Video Bible Commentary observes: "God's emphatic 'No' asserts divine sovereignty — He defines the terms of the promise." The repetition of "I will" (15 times in Genesis 17 alone) shows this is initiated and sustained by God alone.
2. Generational Continuity
Genesis 26:3–4 — "I will give you and your descendants all these lands, and I will confirm the oath I swore to your father Abraham. I will make your descendants as numerous as the stars of heaven and give them all these lands, and through your offspring all nations on earth will be blessed."
The Bible Study on Genesis 26 (Coulter) explains: "God also reaffirms the covenant that He made with Abraham, and promises to bless Isaac and his descendants with the land, the seed, and the blessing. God reminds Isaac that He is a covenant-keeping God, and that He will not break His oath or His word."
Genesis 26:24 — "The LORD appeared to him that night and said, 'I am the God of your father Abraham. Do not be afraid, for I am with you; I will bless you and will make your descendants as numerous as the stars of the sky for the sake of my servant Abraham.'"
The BibleSays commentary notes: "God reaffirmed the covenant first made with Abraham, pledging the same commitment to Isaac" — the covenant people survive even when individual members fail (as Isaac himself does in vv. 7–13, deceiving Abimelech about Rebekah).
Genesis 22:17–18 — "I will surely bless you and will make your descendants as numerous as the stars in the sky and as the sand on the seashore. Your descendants will take possession of the cities of their enemies. Through your offspring all nations on earth will be blessed, because you have listened to me."
The Forerunner Commentary emphasizes: "God does not condition His fulfilling this promise on any expected behavior by Abraham. Note, too, that this promise has the effect of an oath, in that God swears by Himself."
3. Irrevocable Oath (Double Guarantee)
Genesis 22:16 — "By myself I have sworn, declares the LORD, that because you have done this and have not withheld your son, your only son."
Ellicott's Commentary: "This solemn interposition of an oath (Hebrews 6:17), of which the present is the sole instance in Holy Scripture, plainly indicates that this trial of Abraham's faith was of no common kind." Gill's Exposition: "Aben Ezra observes is a great oath, and abides for ever; for because he could swear by no greater, he swore by himself, his own nature, perfections, and life."
Hebrews 6:17–18 — "So when God wanted to make the unchanging nature of his purpose very clear to the heirs of the promise, he guaranteed it with an oath, so that they could be perfectly sure that no one could overturn what had been confirmed by two unchangeable things, in which it is impossible for God to lie. Therefore it is with great confidence that we who have fled to take refuge in the hope set before us may seize on it."
Philip Hughes (Precept Austin): "God in his goodness desired to show more convincingly, to underline, as it were, with a double assurance, the unchangeable character of his purpose; and to this end he interposed with an oath. This he did for the sake not only of Abraham but also of all the heirs of the promise, whose line starts with Abraham and continues on through Isaac."
Leon Morris: "Mesiteuo has the idea of 'mediate,' which often means 'interpose,' 'stand between.' But here the idea is rather that of 'stand as guarantor.' God appears, so to speak, in two characters, the giver of the promise and then its guarantor."
Dr. Constable's Expository Notes: "God swearing by Himself signifies that He binds His word to His character. Thus God gave Abraham double assurance that He would indeed deliver what He had promised."
Berean Bible Church (Hebrews 6:13–20): "God, then, guaranteed his trustworthiness through two immutable or unchangeable things: His word of promise and his oath in confirmation of that word."
With all of that said, it shows that God/Jesus made an irrevocable promise to Abraham and Isaac. The Old Testament says that God is the God of Abraham, Isaac, and Jacob (renamed Israel). Through these three, God will redeem the genetic seed of Israel. Just like the rest of us Gentile Christians who are preserved by Grace through Faith, that was promised and given to us by God. We didn't receive faith on our own. God gave that to us as well, not just the grace that comes with it.