Gentiles, by faith, are grafted in among Israel (the Israel of God) as Israelites.  It’s not by blood.  It never has been.  That’s why John the Baptist said in Matthew 3:9:  “And think not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham.”  Could God raise up children unto Abraham out of stones?  Yes.