Romans 4:12

‘And the father of circumcision to those who not only are of the circumcision, but who also walk in the steps of that faith of our father Abraham which he had in uncircumcision.'

Nor is Abraham to be seen as the father of all who are circumcised. (As Jesus would point out to the Pharisees who claimed to be sons of Abraham, ‘you are of your father the Devil' - John 8:39). He is rather to be seen as the father of those of the circumcised who walk in the same steps of faith as did Abraham, and whose faith therefore is of a kind that results in them being reckoned as in the right before God. It would be wrong therefore to see circumcision as putting a man in the right in the eyes of God.

This, of course, ties in with his previous argument in Romans 2:25 where he pointed out that the true circumcision were those whose hears had been circumcised, in other words those in whose hearts God had worked by His Spirit.