The examples of Abraham and David, both Jews, led to the question Paul voiced in the next verse ( Romans 4:9). The apostle pointed out that when God declared Abraham righteous the patriarch was uncircumcised. He was a virtual Gentile. Fourteen years later Abraham underwent circumcision ( Genesis 17:24-26). His circumcision was a sign (label) of what he already possessed. This point would have encouraged Paul"s Jewish readers, who made so much of circumcision, to keep it in its proper place as secondary to faith. Paul used Abraham as more than an example of faith. [source][source][source]
"As the recipient and mediator of the promise, his experience becomes paradigmatic for his spiritual progeny." [1][source]