Genesis 17

14 Any male who was not circumcised would be cut off from his people—that is, cut off from all covenant blessings. For that person the covenant would no longer apply.

15–18 To signify Sarai’s new status under the covenant, God changed her name to Sarah⁷⁵ (verse 15). God further promised that Sarah would have a son, even though she was nearly ninety years old and long past the age of childbearing (Genesis 18:11). As God had foretold concerning Abraham (verses 5–6), so He foretold concerning Sarah that she would become the mother of nations and that kings would come from her (verse 16).

To Abraham all this seemed amazing; he laughed. He didn’t laugh in mockery or disbelief (Romans 4:18–21); he was lying facedown in an attitude of worship (verse 17). Rather he laughed in surprise and wonder. But he already had a son by Hagar—the boy Ishmael—who was then thirteen years old (verse 25); if only God would give the covenant blessing to him (verse 18), then there would be no need to have a son by Sarah.

19 But God had His own plan; He had already chosen which son would inherit the covenant blessing: it would be Sarah’s son, and his name would be Isaac.⁷⁶

20–22 But God heeded Abraham’s request that Ishmael be blessed also. God repeated the promise He had made to Hagar (Genesis 16:10): “I . . . will greatly increase his numbers” (verse 20). Not only that, God would also make Ishmael into a great nation; he would become the father of twelve rulers—a promise that was exactly fulfilled (Genesis 25:13–16).

However, God would establish His covenant with Isaac, not Ishmael. Notice that Isaac did nothing to deserve this honor; he hadn’t even been born. God’s choices are made solely on the basis of His grace, not on the basis of man’s merits (Romans 9:6–13; Galatians 4:21–23,28–31).

God promised that within a year, Sarah would give birth to Isaac. And it came to pass exactly as He had promised (Genesis 21:1–3).

23–27 On that very day Abraham obeyed God and circumcised every male in his household. Again we see that Abraham’s life was characterized by faith and prompt obedience: no further questions, no further delay. Notice in verse 27 that even those bought from a foreigner⁷⁷—those who were not Abraham’s offspring—were to be circumcised. These were Gentiles; and so, from the beginning, we can see that God intended His covenant blessing to be passed on to the Gentiles—to all peoples on earth (Genesis 12:3).