Albert Barnes Commentary Romans 2:28

"For he is not a Jew who is one outwardly; neither is that circumcision which is outward in the flesh:" — Romans 2:28 (ASV)

For he is not a Jew, etc. He who is merely descended from Abraham, and is circumcised, and externally conforms to the law only, does not possess the true character, and manifest the true spirit, contemplated by the separation of the Jewish people. Their separation required much more.

Neither is that circumcision. etc. Neither does it meet the full design of the rite of circumcision, that it is externally performed. It contemplated much more. See Romans 2:29.