A Great Partner for a Great Endeavor
Abraham acts as if he alone is God's chosen, but Sarah tells him otherwise, and God agrees with her.
The angel who gallantly informs Abraham and Sarah of the impending birth of their son, Isaac, is something of a Johnny-come-lately. God has already informed Abraham of Isaac's future birth at the end of last week's portion:
God: "Sarai your wife shall no longer be called Sarai, Sarah is her name. And I will bless her and I will give you a son from her and I will bless her so that she will become nations, kings of peoples will come from her."
Abraham: "Would that Ishmael live before you!" [In short, "No thanks, I don't need another son. I already have Ishmael."]
God responds that Sarah will bear Abraham a son in a year's time. He will be called Isaac, and he will be the covenantal son, the one who maintains the special relationship with God that Abraham started (Genesis 17: 15-21).
This exchange provides insights into Abraham's understanding of his family and his covenant with God, and it sets the stage for our story this week.
The first factor to note is that once Abraham has his son Ishmael--whom he had with Hagar, Sarah's maidservant, he believes he has no need for any other sons. It does not matter to him that his wife Sarah has been barren for 90 years and was so desperate for a child that she tried to have one through her surrogate Hagar (a plan that went horribly awry in Genesis 16).
Not only is Abraham unenthusiastic about the portent of Isaac's coming, even more strikingly, he does not share the information with Sarah. Although the angel's tidings of Isaac's birth is old news for Abraham, Sarah is apparently shocked by the revelation. She laughs to herself, saying, "After I have ceased menstruating and my master is elderly." The defining feature of Sarah has been her inability to have children (see Genesis 11:30). After years of waiting and despair, she is at long last promised a son in the upcoming year, and Abraham does not bother to tell her.
Why is Abraham so lukewarm about Isaac's arrival? The answer lies in Abraham's understanding of his covenant with God.