Charles Ellicott Commentary Genesis 17:16

"And I will bless her, and moreover I will give thee a son of her: yea, I will bless her, and she shall be [a mother of] nations; kings of peoples shall be of her." — Genesis 17:16 (ASV)

A son ... of her. —This is the first place where it was definitely promised that Abram’s heir should be Sarah’s own son. This must be remembered in estimating the conduct of Abram and Sarah in the matter of Hagar. They had long waited, and hoped, before taking measures of their own for the fulfillment of the promise. The rest of the verse should be translated, “she shall become (grow into) nations: kings of peoples shall become of her, that is, “shall spring from her.””