What Does Genesis 17:16 Mean?

"I will bless her and will surely give you a son by her. I will bless her so that she will be the mother of nations; kings of peoples will come from her." The promise shifts to specify what Sarah's blessing will accomplish: a son through her specifically, and through that son the same expansion to nations and kings that was promised to Abraham in verses 4-6. The offspring who will be the father of many nations must be Sarah's son, specifically Abraham's son. The son of Hagar is Abraham's biological son; he is not the child the covenant promise requires. The covenant heir must be born of Sarah.

The double "I will bless" in this verse, first "I will bless her" and then "I will bless her so that," emphasizes that the promised son is entirely God's gift through Sarah's barren body. Two acts of divine blessing are required: the blessing of her person and the blessing that produces the specific outcome. Neither Sarah's body in its current state nor any natural process can produce what is promised here. The God of the blessing is the God who acts where biology has stopped. El Shaddai, introduced in verse 1 of this chapter, is the name for exactly this kind of engagement with human impossibility.

"Kings of peoples will come from her" is the parallel to "kings will come from you" (verse 6). Sarah is named as the mother of royal lines, specifically as the vehicle for Abraham's covenant. The Davidic line, from which Jesus descends through the biological chain of Israelite history, traces through the son who comes from Sarah, through Isaac to Jacob to Judah and through the centuries of Israel's kings to the Bethlehem stable where the king of kings was born. Every king in that chain was Sarah's descendant by the explicit promise of this verse.