For this reason, the promise [i.e., of being made right with God] comes through faith [in God], according to His unearned favor, so that it may be [given] with certainty to all of Abraham's descendants. The promise is given not only to those [who live] under the law [i.e., the Jews], but also to [all] those [who live] by faith, like Abraham. Abraham is the [spiritual] father of all of us [believers],

This means that it is not the physical descendants [of Abraham] who are God's children, but it is the children [born] according to [God's] promise who are [Abraham's true] descendants.

Neither are all [Jewish] people children [of God], [simply] because they are Abraham's descendants. But [Gen. 21:12 says], "It is through Isaac that you [i.e., Abraham] will have descendants."

Abraham's faith did not become weak [even though] he was about one hundred years old and considered his body almost dead and Sarah's womb incapable of conceiving a child.

Is this blessing experienced by the circumcised ones [i.e., the Jews only] or by the uncircumcised ones [i.e., the Gentiles] also? We are saying, "Abraham's faith was credited to him for righteousness."

For if Abraham had been made right with God by doing good deeds he would have had something to boast about, but not in God's presence.