See
John 1:13 children born not of natural descent, nor of human decision or a husband's will, but born of God.
Did you read how the scripture says 'not of natural descent'?
Natural decent is about those to whom we are blood related.
The written Word of God says NOT of natural descent. That means it does not matter if someone is blood related to Abraham.
See how the scripture says not of human decision?
That is about a human cannot say they are saved by just saying it.
See how the scripture says not of a husband's will?
That is about a husband not being able to have his wife become a Jew, or even a Christian, by converting her with certain rituals.
In the past, a Jew could marry and she performs the practices of Judaism, and so become a Jew and a child of God...this is no more now since Jesus.
Being born of God is how we are now saved. We are born of God by receiving the Holy Spirit. We receive the Holy Spirit by asking Jesus to save us, after we repent of our sins and call on him. When Jesus saves us and gives us his Holy Spirit that is when we are born again.