Bible Notes Online - Genesis 17 - ESV
Commentary

v1-2
Another 13 years pass; it is now 24 years since Abram left Haran, see Genesis 12:4. The Lord has been teaching him, line upon line, precept upon precept. As elsewhere (Genesis 15:7), the Lord reminds Abram who He is, and then of his on-going responsibility, and then of the covenant. Even though Abram has fallen short in some respects, God's promises remain.

v3-6
Abram's new name, Abraham, speaking of God's promise; a father of many nations; he will be exceedingly fruitful, and nations and kings will come from him. Abram has been a 'great father', but now God has something much greater for him.

v7-8
The covenant includes Abraham's descendants, and includes the land of Canaan; over all comes the promise, "I will be their God".

v9-14
The sign of circumcision, see Romans 4:10-12. Abraham has already believed God, and now he receives the sign of circumcision, a testimony of belonging to the Lord, of being a partaker in the divine covenant, Joshua 5. This is a physical, permanent, sign; there is a cost in following the Lord. There is the rolling away of the flesh, as at Gilgal (Joshua 5.9), a total dependence upon the Lord.

In chapter 34 this precious and important thing is abused by Levi and Simeon.

v15-17
Sarai is also included in the promises, with a new name, Sarah. She will be the mother of nations, and kings of peoples will come from her. At this Abraham laughed, Genesis 18:12; 21:6-7. Here is God making promises for the impossible. Abraham is virtually 100 years old, Sarah 90; even in these days this was impossible, not just unusual. Contrast chapter 5, where a number of men were born to fathers over 100 years old. By chapter 11, after the flood, this has changed.

v18-22
The Lord insists that Isaac, not Ishmael, will be in the line of His promises. There are other promises concerning Ishmael which are fulfilled, Genesis 16:11-12; 25:12-16.

v23-27
Immediate obedience, as Abraham circumcises his whole household.