Abraham’s Two Sons (Genesis 21)

Abraham Study Guide (Week 12)


The LORD visited Sarah as he had said, and the LORD did to Sarah as he had promised. (Genesis 21:1)

Know therefore that the LORD your God is God, the faithful God who keeps covenant and steadfast love with those who love him and keep his commandments, to a thousand generations. (Deuteronomy 7:9)

Now you, brothers, like Isaac, are children of promise. (Galatians 4:28)


From the first moment that God appeared to Abraham, He promised the patriarch a son, an offspring that God would both bless and use to bless others. For the childless man and his wife, Sarah, this must have been like hearing a splash of water in the desert. But then God waited twenty-five years. Along the way, He continued to promise Abraham that his son would come. Eleven years into waiting, Abraham tried to help God by impregnating his wife’s servant, yet God specified that He would give Abraham a child via Sarah. Still, after numerous renewals of the promise, Abraham and Sarah still had no child, until now.

Following twenty-five years of God promising the birth of Isaac, Abraham and Sarah finally have a child! The joy of the moment is captured in Isaac’s very name—which means “laughter”—because the utter impossibility of his birth is laughable notion. Yet as God told Sarah earlier, nothing is too hard for the LORD. But the chapter is not all joyful. The birth of Isaac immediately creates tension between Sarah and Hagar and Ishmael. In resolving this conflict, Sarah demands for Hagar and Ishmael to be cast out, but God still provides for Hagar and Ishmael in the wilderness. Finally, the chapter ends with Abraham and Abimelech making a treaty with one another.

At first glance, this chapter can seem rather disjointed, especially with the Abraham’s covenant with Abimelech occurring at the end. However, I believe the overall message of this chapter is that God is faithful. Isaac’s birth displays God’s faithfulness to keep His promise, even if doing so requires the working of the impossible. God’s provision for Hagar and Ishmael in the wilderness is a sign of His faithfulness to do what He has spoken. God’s faithfulness is also revealed in Abraham’s treaty with Abimelech, emphasizing that Abimelech would not become an enemy of Abraham later.

Read verses 1-7 and discuss the following.

  • After waiting for twenty-five years, the LORD finally blesses Abraham and Sarah with a child in their old age, just like He promised. What does the birth of Isaac teach us about the character and attributes of God?

Read verses 8-14 and discuss the following.

  • Isaac’s birth quickly causes a tension to grow between Sarah and Hagar. When Sarah finds Ishmael laughing (likely in mockery of Isaac), she demanded that Abraham cast out Hagar and Ishmael. In Galatians, Paul uses this account as an allegory. What is Paul’s point and its significance in Galatians 4:21-31?

Read verses 15-21 and discuss the following. 

  • In the desert, Hagar and Ishmael appear to be dying of thirst, but the LORD intervenes by showing them well of water. God renews his promise from chapter 16 to make Ishmael into a great nation. How does this act display the faithfulness of God?

Read verses 22-34 and discuss the following. 

  • Having seen in the previous chapter God’s blessing upon Abraham, Abimelech and his army commander desire to make a treaty with Abraham. What does this say about how outsiders perceived Abraham? Is this similar to how non-Christians should see us?


  • Like Abraham with Abimelech, consider how non-believers perceive your relationship with the LORD and in what ways they might declare, “God is with you.”
  • As with showing Hagar and Ishmael the well of water, recall times when God has provided for you and pray with gratitude.

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