Romans 2:28

A man is not a Jew if he is only one outwardly, nor is circumcision merely outward and physical.

(v28, NIV)

Paul has just explained how circumcision can become uncircumcision and how uncircumcision can become circumcision. There were probably many objections to this and how this could occur. Well, clearly Paul isn't saying that there is an outward transformation occurring, changing from one to the other. Physically, if you were to be circumcised, I don't think there is any way for that to be undone. In circumcision, you remove, and I don't think it grows back. However, the point is that circumcision is not merely outward and physical. So, if circumcision were only outward and physical, then Paul would be wrong in what he is saying. However, this is not the case, and there is more to circumcision than a physical mark. Now, Paul makes a similar statement saying how a Jew is not simply a Jew if he is one outwardly. Now, this is getting personal. Paul has been talking about circumcision, but now he is switching gears and directing towards Jews in general. Sure, most would have associated circumcision with merely outward and physical appearances, but that is not true. Similarly, most would have associated Jewishness with merely outward appearances, like your parents or how you look. However, is that really the case? Being a Jew does not constitute only outward appearances.