Can you show me which verse(s) support your assertion?
Their only hope is to receive the gospel from faithful believers.
For as ye in times past have not believed God, yet have now obtrained mercy through their unbelief: Even so have these also now not believed, that through your mercy they also may obtain mercy. For God hath concluded them all in unbelief, that he might have mercy upon all. (Romans 11:30-32)
We are definitely to be faithful to share the gospel with ALL non-believers.
The point is that he isn't done with Israel or the Jewish people. Far from it according to Romans 11. Romans 11:1-2 "I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin. God hath not cast away his people which he foreknew..." And in the very end of the age an entire remnant of Israel will witness the Lord's return and cry "Baruch Haba Bashem Adonai!"