Don't suppose for a moment, though, that God's Word has malfunctioned in some way or other. The problem goes back a long way. From the outset, not all Israelites of the flesh were Israelites of the spirit.
It wasn't Abraham's sperm that gave identity here, but God's promise. Remember how it was put: "Your family will be defined by Isaac"?
That means that Israelite identity was never racially determined by sexual transmission, but it was God-determined by promise.
Remember that promise, "When I come back next year at this time, Sarah will have a son"?
And that's not the only time. To Rebecca, also, a promise was made that took priority over genetics. When she became pregnant by our one-of-a-kind ancestor, Isaac,
and her babies were still innocent in the womb - incapable of good or bad - she received a special assurance from God. What God did in this case made it perfectly plain that his purpose is not a hit-or-miss thing dependent on what we do or don't do, but a sure thing determined by his decision, flowing steadily from his initiative.
God told Rebecca, "The firstborn of your twins will take second place."
Later that was turned into a stark epigram: "I loved Jacob; I hated Esau."
Is that grounds for complaining that God is unfair? Not so fast, please.
God told Moses, "I'm in charge of mercy. I'm in charge of compassion."
Compassion doesn't originate in our bleeding hearts or moral sweat, but in God's mercy.