Romans Chapter 2:141 The nature of man, as created by God was originally good and corresponded with God and with His law.  Although it was poisoned by the fall, this good nature remains within man.  Hence, if anyone lives according to his nature and does by his nature the things of the law, the evil in him will be restricted. 
Romans Chapter 2:151 Man's conscience corresponds with the God-created human nature and enables man to know what God justifies and what he condemns. 
Romans Chapter 2: 281 Any religious practice, such as circumcision, that is merely an outward form is not real. 
As Paul preached throughout his life, "what advantage do the Jews have"?