This means that not all of Abraham’s descendants are God’s true children. Abraham’s true children are those people that become God’s children because of the promise God made to Abraham.
And don’t think that you can boast and say to yourselves, ‘Abraham {\cf2\super [39]} is our father.’ I tell you that God could make children for Abraham from these rocks here.
These children were not born like little babies are born. They were not born from the wish or plan of a \{mother and\} father. These children were born from God.
Everything that God made is waiting with excitement for the time when God will show the world who his children are. The whole world wants very much for that to happen.
Abraham was too old to have children. And Sarah was not able to have children. But Abraham had faith in God, and so God made them able to have children. Abraham trusted God to do the things he promised.