Then God said to Abraham, “As for Sarai your wife, do not call her Sarai, for her name is to be Sarah.
15. As for Sarai thy wife God now promises to Abraham a legitimate seed by Sarai. She had been (as I have said) too precipitate, when she substituted, without any command from God, her handmaid in her own place: Abraham also bad been too pliant in following his, wife, who foolishly and rashly wished to anticipate the design of God; nevertheless, their united fault did...
Here is, I. 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, Gen 17:16. Note, 1. God reveals the purposes of his good-will to his people by degrees.
Commenting on Genesis 17:15-22
And God said unto Abraham,.... After he had changed his name, and given him the covenant of circumcision: as for Sarai thy wife, thou shalt not call her name Sarai, but Sarah her name shall be; her former name Sarai signifies "my princess", or rather "princesses", being to him in the room of many, and better than ten thousand; yet only a princess to him...