…your wife Sarah will bear you a son, and you will call him Isaac. I will establish my covenant with him as an everlasting covenant… Genesis 17:19
Through years of waiting for God to fulfill his promise of a son, Abram struggles between keeping faith and taking action himself. Ten years after the promise is given, Abram and Sarai conspire together to produce a child through their maid, Hagar. Their plan is unfaithful in every way and produces a son, Ishmael, who brings conflict, not blessing, into the family. Thirteen years after Ishmael’s birth the promised child is finally born to Sarai, now called Sarah, and Abram, now called Abraham. God changes their names to match the reality of their new roles as mother and father of a nation of kings and priests.
God makes a tremendous distinction between Ishmael and Isaac. He tells Abraham, “my covenant I will establish with Isaac.” A few years later, speaking to Abraham about Isaac, God calls him “your son, your only son, Isaac, whom you love.” If there was any doubt about why God insisted on fulfilling his plan through Isaac, the apostle Paul made it plain in the book of Romans: