Romans 4:11-13, 16

He received the sign of circumcision, a seal or confirmation of the righteousness which he had by faith while [he was still] uncircumcised—this was so that he would be the [spiritual] father of all who believe without being circumcised—so that righteousness would be credited to them, and [that he would be] the [spiritual] father of those circumcised who are not only circumcised, but who also walk in the steps of the faith of our father Abraham which he had before he was circumcised. For the promise to Abraham or to his descendants that he would be heir of the world was not through [observing the requirements of] the Law, but through the righteousness of faith. [Gen 17:4-6; 22:16-18]

Therefore, [inheriting] the promise depends entirely on faith [that is, confident trust in the unseen God], in order that it may be given as an act of grace [His unmerited favor and mercy], so that the promise will be [legally] guaranteed to all the descendants [of Abraham]—not only for those [Jewish believers] who keep the Law, but also for those [Gentile believers] who share the faith of Abraham, who is the [spiritual] father of us all