John Gills Exposition of the Bible Commentary - Genesis 17:21
But my covenant will one establish with Isaac ,.... The covenant of circumcision; for though Ishmael was circumcised, and his posterity practised that rite, yet it was not enjoined them of God; nor was it to them, or served the same purpose as to the Israelites; and particularly the promise of the land of Canaan, made in that covenant, belonged only to the posterity of Isaac, and to those only in the line of Jacob, and especially that of the Messiah springing from him, which circumcision had... read more
Matthew Henry's Complete Commentary - Genesis 17:15-22
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. God had told Abraham long before that he should have a son, but never till now that he should have a son by Sarai. 2. The blessing of the Lord makes fruitful, and... read more