8In other words, it is not the children by physical descent who are God’s children, but it is the children of the promise who are regarded as Abraham’s offspring.
8That is, it is not the children of the body [Abraham’s natural descendants] who are God’s children, but it is the children of the promise who are counted as [Abraham’s true] descendants.
8In other words, God’s children are not just in the family line of Abraham. Instead, they are the children God promised to him. They are the ones considered to be Abraham’s children.
8This means that not all of Abraham's children are really God's children. It is only those children who were born as a result of God's promise. They are the people that God calls true descendants.