“Then what advantage has the Jew? Or what is the value of circumcision?”
Paul has been arguing that the Holy Spirit’s inward work of creating new hearts in Gentiles makes them more Jewish than Jews simply trying to obey the Law. The logical question that should follow is, “Well, then, what is the value of salvation for a Jew in terms of eternal life?"
It’s a question for all of us to ponder too: What value is there in trying to work our way to salvation? The answer is, “None!” God is perfectly holy. We are not. Our vain attempts to obey the law show how imperfect and fallen we really are.
Therefore, we desperately need a Savior who changes us from the inside/out. That’s the work of the Holy Spirit. That was the source of Paul’s question.