Commentary - Genesis 17:15-22

Bird's-eye view

In this passage, the Lord, having just renamed Abram to Abraham and established the covenant of circumcision, now turns His attention to the matriarch of the promise. Sarai's name is changed to Sarah, and the promise of a son is made explicit, emphatic, and exclusive to her. This is God's direct and gracious course correction to Abraham and Sarah's misguided attempt to fulfill the promise through Hagar. The focus here is on the sovereign, elective grace of God. The covenant promise will not be accomplished through human ingenuity or natural means, but through a divine miracle: life from a dead womb. Abraham's reaction of laughter, a complex mixture of astonishment and faith, is met not with rebuke, but with God naming the promised child Isaac, meaning "laughter." God distinguishes sharply between the immense common grace blessing on Ishmael and the unique, redemptive, everlasting covenant that will be established with Isaac. This is a foundational text for understanding the nature of God's elective covenant and the principle of salvation by grace alone.

This is the moment the covenant train gets put back on the main line. The Ishmael excursion, born of impatience and a failure to trust, is now addressed. God does not berate Abraham for his earlier lapse but simply overrides it with a promise so specific and miraculous that it cannot be mistaken for anything other than a pure act of God. The promise will come through Sarah, and Sarah alone. This sets the stage for the entire drama of redemption, where God consistently chooses the weak, the barren, and the foolish to accomplish His purposes, so that no flesh may glory in His presence.

Outline

Context In Genesis

This section is the heart of the covenant ceremony in Genesis 17. It follows directly upon God's declaration of Himself as El Shaddai (God Almighty) and the changing of Abram's name to Abraham, father of a multitude. The sign of the covenant, circumcision, has just been instituted (17:1-14). Up to this point, the promise of a seed has been general. Abraham, in a moment of flawed faith, had tried to secure this heir through Hagar, resulting in the birth of Ishmael (Genesis 16). Now, thirteen years after Ishmael's birth, God appears to Abraham to clarify the precise line through which the covenant of grace will flow. This passage corrects the human error of chapter 16 and sets the stage for the miraculous birth of Isaac in chapter 21, the testing of Abraham in chapter 22, and the entire subsequent history of Israel.

Key Issues

The Great Correction

One of the most comforting things about the patriarchal narratives is that God's covenant is not dependent upon the flawless performance of the patriarchs. Abraham is the father of the faithful, but he is a man who stumbles. The whole affair with Hagar and Ishmael was a humanly-engineered plan, a work of the flesh, born out of a crisis of faith in God's timing. It was an attempt to "help God out." And here, God does not rake Abraham over the coals for it. He simply and majestically announces His real plan, the one He had all along.

This is not Plan B. God's intention was always to bring the heir of promise from Sarah's barren womb. The Ishmael episode was a detour, but God, in His sovereignty, uses even our detours. He shows Abraham the difference between a work of the flesh (Ishmael) and a work of the Spirit (Isaac). One is born according to natural means, the other by a supernatural promise. This is precisely the distinction the Apostle Paul will later pick up in Galatians 4, where he uses Hagar and Sarah as an allegory for two covenants: one of slavery to the law, and one of freedom in Christ. God is teaching Abraham, and us, that the covenant of grace is a covenant of grace from start to finish.

Verse by Verse Commentary

15 Then God said to Abraham, “As for Sarai your wife, you shall not call her name Sarai, but Sarah shall be her name.

Just as Abram's name was changed to reflect his covenant role, so now is Sarai's. The change is subtle in English but significant. Sarai means "my princess," which has a personal, possessive sense. She is Abram's princess. But Sarah means "princess" in a more absolute sense. She is not just the princess of a clan; she is a princess of nations. God is elevating her status from a private individual to a public, foundational figure in redemptive history. She is being formally installed in her covenant office as the mother of the promised line.

16 And I will bless her, and indeed I will give you a son by her. Then I will bless her, and she shall be a mother of nations; kings of peoples will come from her.”

The blessing is stated and then restated for emphasis. First, God says, "I will bless her." How? "I will give you a son by her." This phrase is the linchpin. It is the direct correction to the Hagar plan. The heir will not come from a surrogate, but from the barren matriarch herself. The blessing is then expanded: she will not just be the mother of one son, but a "mother of nations." Kings will come from her. This promise mirrors the promise given to Abraham. They are joint heirs of this grace, and the covenant will flow through their union, a union that God Himself will make miraculously fruitful.

17 Then Abraham fell on his face and laughed and said in his heart, “Will a son be born to a man one hundred years old? And will Sarah, who is ninety years old, bear a son?”

Here is one of the great laughs of Scripture. How are we to take it? Is this the cynical laugh of unbelief? Not at all. The New Testament is our inspired commentary here, and Hebrews 11 commends Abraham's faith, not his doubt. This is the laughter of sheer, unadulterated astonishment. He falls on his face in worship, and the worship is so joyful, so overwhelmed by the glorious absurdity of God's promise, that it erupts in laughter. He is not mocking God; he is marveling at Him. The questions he asks in his heart are not the questions of doubt, but the questions of wonder. He is mentally holding up the biological reality (he is 100, she is 90) against the divine promise, and the glorious mismatch makes him laugh with joy.

18 And Abraham said to God, “Oh that Ishmael might live before You!”

This is not Abraham rejecting the new promise about Isaac. This is the tender heart of a father. He has just been given this incredible news, and his first thought is for the son he already has, the son he has raised for thirteen years. To "live before You" is a plea for God's favor and blessing. Abraham is essentially saying, "Lord, I receive this new promise about Isaac with joy. But please, in all of this, do not forget my boy Ishmael. Let him have a place in Your goodness." It is a beautiful, pastoral, fatherly prayer.

19 But God said, “No, but Sarah your wife will bear you a son, and you shall call his name Isaac; and I will establish My covenant with him for an everlasting covenant for his seed after him.

God's response is a firm but gracious clarification. The "No" is not a rejection of Ishmael's well being, but a rejection of the idea that Ishmael could be the covenant heir. God is drawing a sharp, bright line. The covenant is not a matter of human sentiment or natural birth order; it is a matter of divine, sovereign election. God then does something remarkable. He takes Abraham's laughter of astonishment and consecrates it. He commands Abraham to name the boy Isaac, which means "he laughs." Every time Abraham would call his son's name, he would be reminded of this moment, this impossible promise, and the joyful laughter that God not only accepted but memorialized. The covenant with Isaac and his seed is to be everlasting, which points ultimately to Christ.

20 As for Ishmael, I have heard you; behold, I will bless him and will make him fruitful and will multiply him exceedingly. He shall become the father of twelve princes, and I will make him a great nation.

God is not cruel. He assures Abraham that his fatherly prayer for Ishmael has been heard. Ishmael will receive a blessing, and it is a magnificent blessing. He will be fruitful, multiply exceedingly, father twelve princes, and become a great nation. This is a massive bestowal of common grace. God will give him land, descendants, and political power. But it is not the covenant. This is a crucial distinction that runs throughout Scripture. God gives good gifts to all men, but He gives Himself in covenant to His elect.

21 But My covenant I will establish with Isaac, whom Sarah will bear to you at this season next year.”

Lest there be any confusion, God repeats the central point with the strong adversative "But." The covenant, the unique, redemptive, everlasting relationship, is for Isaac. God uses the word "establish," meaning to make it stand firm. This is God's work, not Abraham's. And to anchor this seemingly impossible promise in reality, God gives a deadline. It will happen "at this season next year." This is a testable, falsifiable promise. God is putting His own credibility on the line. In about a year, there will be a baby named Laughter, or God is not God.

22 So He finished talking with him, and God went up from Abraham.

The divine audience concludes. This has been a theophany, a direct, personal appearance of God to Abraham. God has spoken, the terms have been clarified, the promise has been made specific. Now, the visible presence of God departs, and Abraham is left with the staggering weight and glory of what he has just heard, and the immediate, practical task of obeying the command of circumcision for himself and his entire household, including Ishmael.

Application

The temptation to raise up Ishmaels is a perennial one for the people of God. When God's promises seem slow in coming, or when the means He has appointed seem weak and foolish to the world, we are tempted to resort to our own cleverness. We try to build the church through marketing schemes, political maneuvering, or compromising with the culture. We try to fix our lives through self-help programs that bypass the hard work of repentance and faith. These are all Ishmaels, sons of the flesh.

God's word to us in this passage is to stop. His covenant is established with Isaac, the son of promise, a type of our Lord Jesus Christ. Salvation comes not through our striving, but through a miracle of God, life from the dead. Our part is to believe the promise, even when it seems as absurd as a ninety-year-old woman conceiving a child. We are to trust in the finished work of the true Isaac, Jesus, who was born miraculously, died on a cross, and was raised from the dead. And when we are overwhelmed by the sheer grace of it all, it is okay to fall on our faces and laugh. Our God has a wonderful sense of humor, and His name is glorified when His people are filled with an astonished joy at the glorious impossibility of His salvation.