21:1–7 The report of Isaac’s birth concludes the story of Sarah’s barrenness begun in 11:27–32. The covenantal arrangement is underscored: God keeps His promise to give Abraham a son by Sarah (vv. 1–2; 17:1–6, 15–16; 18:1–15), and Abraham responds in obedience by naming him Isaac (v. 3; 17:19) and circumcising him (vv. 4, 5; 17:9–14), while Sarah responds with praise (vv. 6, 7).