Not Only, But Also

Romans 4:16-17 (ESV Strong's)

16 That is why it depends on faith, in order that the promise may rest on grace and be guaranteed to all his offspring—not only to the adherent of the law but also to the one who shares the faith of Abraham, who is the father of us all, 17 as it is written, “I have made you the father of many nations”—in the presence of the God in whom he believed, who gives life to the dead and calls into existence the things that do not exist.

Those who remain under the law are offspring of Abraham. Those who share the faith of Abraham are also his descendants. God blesses both. They both serve the one God, but in different ways according to their revelation. 

The revelation of faith is centered in the relationship between an individual and the Lord. United in the Spirit, we stand alone before the throne of God.