Genesis 17 is the great transition in the story of Abraham. Just prior, he has fathered a child with Hagar. It’s the high point of the story so far: Abram, the Big Father, finally has a son. But it’s not the son who will carry the promise. It’s the best flesh can do, but it’s still the best flesh can do. Flesh can do no better than father sons of the slave-woman.

Once flesh is cut off, though, Abram can be Abraham, and instead of fathering a slave-son with the slave-woman, he fathers a Spirit-son with the free woman.