The Birth of Isaac and the Expulsion of Ishmael: Sarah bears the child of promise. In light of this couple’s waiting twenty-five years for God’s promise to be fulfilled, it is amazing how matter-of-fact is the report of Isaac’s birth. Directly following this happy, triumphal account comes the report of an ugly incident in which Sarah demands that Hagar and Ishmael be expelled from the household. The latter incident receives more coverage because it relates the drastic rearrangement the birth of the son of promise causes in Abraham’s household.

The two episodes in this section are the birth of Isaac (vv. 1–7) and the expulsion of Hagar and Ishmael from Abraham’s house (vv. 8–20). A play on the name Isaac binds the two accounts. In the first account Sarah laughs because of the gift of Isaac (…