What if some [Jews] were unfaithful? Does their faithlessness nullify the faithfulness of God?
Romans 3:3 ESV

The hypocrisy of some Jews does not devalue the Law and the Prophets or his promises to the patriarchs of Israel, nor does it call into question God's choice of a people.

As Moses said in Deuteronomy 7:7-8, the descendants of Jacob weren’t chosen because they were more deserving or moral than any other people, but because God promised Abraham, Isaac, and Jacob. He will certainly prune them of pathological branches (Romans 11:17), but he will always preserve a remnant for the sake of the patriarchs.