Some day it will be impossible to count the people of Israel, because there will be as many of them as there are grains of sand along the seashore. They are now called “Not My People”, but in the future they will be called “Children of the Living God”.
You are no longer ruled by your desires, but by God's Spirit, who lives in you. People who don't have the Spirit of Christ in them don't belong to him.
Think how much the Father loves us. He loves us so much that he lets us be called his children, as we truly are. But since the people of this world did not know who Christ is, they don't know who we are.
If we obey God's commandments, we will stay united in our hearts with him, and he will stay united with us. The Spirit that he has given us is proof that we are one with him.