But it is not as though the word of God has failed. For not all who are descended from Israel belong to Israel,
Romans 9:6 ESV

Paul says “But it is not as though the word of God has failed” in reference to his dismay at the unbelief of his Jewish kinsmen.

Since God promises that the nation of Israel will one day be restored, does their current unbelief mean that God’s promise has failed? No, every tree needs to be pruned before it branches out and blossoms. The nation itself will remain forever, but individual branches will be pruned. Which branches is not for us to say.