“…he is a Jew who is one inwardly…” Romans 2:29a
It is difficult for a sinful man to grasp the reality of Romans 2:29 for himself because of his inability to see inside himself: in his heart, the place of his affections and will. Sinful people naturally consider them selves to be good, “The heart is deceitful above all things, and desperately wicked; who can know it? Jeremiah 17:9
For the Jew circumcision was the act and symbol of their separation to God and from all other people; Paul explains that the true Jew is one who is separated in his heart and not outwardly. Attending a certain church, wearing special clothes (dress or casual), singing specified songs (traditional or contemporary), and a whole host of incidentals is not circumcision to God – it is a transformation of a sinful heart.
Circumcision that matters to God is circumcision of the spirit (pneuma), which in the Greek has the idea of breath or the living soul of man, that which is beyond the physical body. When a person is separated to God, then his spirit is made alive and his praise goes to God and not men or self.
“…circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.” Romans 2:29b