Genesis 17:15 - Joseph Benson’s Commentary on the Old and New Testaments

Here is the promise made to Abraham of a son by Sarai, that son in whom the promise made to him should be fulfilled, that he should be the father of many nations, for she also shall be a mother of nations, and kings of people shall be of her, Genesis 17:16. Thus God reveals the purposes of his good-will to his people by degrees. He had told Abraham long before that he should have a son, but never till now that he should have a son by Sarai. Sarah shall her name be The same letter is added to her name that was to Abraham's. Sarai signifies my princess, as if her honour were confined to one family only; Sarah signifies a princess, namely, of multitudes.