For if God did not spare the natural branches, neither will he spare you.
Romans 11:21 ESV

The use of “natural branches” refutes any idea that “the Jews” or “Israel” in this context could refer to anything that is completely divorced from the genetic lineage of Jacob. “Natural” Israel at this point had certainly incorporated many foreigners over the centuries, but the entire analogy falls apart if Israel wasn’t substantially made up of actual descendants of Jacob.