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God Fulfills His Promise (Genesis 21:1-34)



In Genesis 20, Abraham again tried the “Sarah is my sister” ruse out of fear for his life (see Genesis 12:10-20). This time, he tried it with Abimelech, king of Gerar. God intervened to assure that Abimelech didn’t touch Sarah, and for the entire time she was in his palace, the women of Gerar couldn’t get pregnant. After the truth came out, Abimelech returned Sarah to Abraham, who in turn prayed for the barren women of Gerar to become pregnant. This begs the question: God can do this for Gerar’s women; when will he do it for Sarah?



God always fulfills his promises at the exact time and in the exact way he planned.



Can you remember what your life was like twenty-five years ago? That’s about the amount of time Abraham has been living with God’s promise of a child. Throughout that time, Abraham has experienced victorious moments of great faith and sinful moments in which his faith falters.

If we were to give a title to Genesis 21:1-7, it would be “At last!” Isaac, the long-promised child of Abraham and Sarah is finally born. The text says that God “visited Sarah as he had said” and did for her “as he had promised”, causing her to give birth “at the time of which” he had told Abraham. These first two verses stress that God is powerful and faithful. Powerful, because he can cause barren, elderly Sarah to give birth. Faithful, because he did what he said he would do in his own time and way. Though the wait was long and often tumultuous, God was never not in complete control.

Verses 3-4 show us Abraham’s faithfulness. He named his newborn son Isaac and had him circumcised on the eight day, both of which were actions that “God had commanded him” (Genesis 17:12, 19). The name “Isaac” means laughter, and whereas Sarah had once laughed in disbelief at the thought of giving birth in her old age, the laughter we see here in verse 6 is one of joy rather than skepticism.

But not everyone is laughing. At least not with joy. Verse 8 moves forward about three years to a great feast “on the day that Isaac was weaned”. At this feast, Sarah saw Ishmael, Hagar’s son, “laughing” (presumably at Isaac). The term used here refers to a malicious, mocking laughter. (Galatians 4:29 says that Ishmael “persecuted” Isaac.) Perceiving Ishmael to be a threat to Isaac’s inheritance, she demands that Abraham send Hagar and Ishmael away (v. 10).

It might seem strange for Genesis to spend seven quick verses recounting Isaac’s birth and then quickly shift and spend fourteen verses talking about Hagar and Ishmael. But even though Isaac is not prominently featured in verses 8-21, his significance is. This section is here to remind us that it is through Isaac, not Ishmael, that God’s promises to Abraham will be fulfilled (v. 12; Romans 9:7). As the firstborn son, it would be a constant temptation for Abraham to consider Ishmael to be the recipient of the inheritance that God told Abraham would be reserved for Isaac. So God commands him to listen to Sarah and send them out.

This is a hard moment for Abraham, who is saying goodbye to his firstborn child forever. And by disinheriting him, he’s sending him out with very few provisions or protection. But while Sarah may have had a more vindictive, “Good riddance!” attitude to their departure, God’s attitude was far different. He had shown great kindness to Hagar once (Genesis 16), and he does so again here. When their supplies run out, God visits Hagar and provides for her and Ishmael’s needs (vv. 15-21). Just because Ishmael wasn’t the “child of promise” didn’t mean that God didn’t care about them. On the contrary, “God was with the boy” (v. 20).

The chapter concludes with another note of God’s faithfulness to Abraham (vv. 22-34). Abimelech shows up again, and realizing how much God has blessed Abraham, he makes a treaty with Abraham, promising that they will deal kindly with each other. Abraham then takes the opportunity to bring up a matter about a well which some of Abimelech’s men had seized from him.

This well dispute and the tamarisk tree Abraham goes on to plant (v. 33) are significant. God has promised this land to him (12:1-9), but for now Beersheba was part of the Philistines’ land (v. 34). By resolving this well dispute, Abraham now claims ownership of a very small piece of the promised land. And by planting the tree, he’s indicated his intent to stay there a long time. So while the chapter begins with God fulfilling a major part of his promises to Abraham by giving him a son (vv. 1-7), it ends with hints that he’ll one day fulfill the promise of land as well. 

  • After a long wait, Abraham is finally a father. If he could have gone back to the moments where his faith faltered, what encouragement do you think he would have given his younger self?
  • God fulfills his promises exactly as he says and exactly when he means to. Where in your life do you need to be reminded of this? How does this truth encourage you?



Genesis 21:1 – “The LORD visited Sarah as he had said, and the LORD did to Sarah as he had promised.”


Click here for a printable version of this discussion guide.