Romans 2:25

‘For circumcision indeed profits, if you are a doer of the law, but if you are a transgressor of the law, your circumcision is become uncircumcision.'

Paul then puts circumcision in perspective. His reply is that circumcision does indeed profit those who are doers of the Law from the heart, for it marks them off as observers of the covenant. It is therefore of great value if they are FULLY observing the covenant into which circumcision has introduced them. As a consequence they would be gaining the full benefit from the covenant that God has made with them (see Deuteronomy 10:16; Deuteronomy 30:6; Jeremiah 4:4; Jeremiah 9:26). On the other hand if they openly and deliberately transgress the Law in any way they are thereby rejecting the covenant relationship, and with the covenant broken their circumcision becomes of no value. It becomes just what circumcision was to most of Israel's neighbours, something of no significance as far as God was concerned. For then it had ceased to be genuine covenant related circumcision, and had become the equivalent of non-circumcision. The Scriptural claim of the need to be circumcised in heart was proof of that. In other words the man who is circumcised should recognise that he has received a special privilege, membership of the covenant, and should as a consequence throw himself into obedience to the covenant, i.e. to the Law. Many Jewish teachers would have agreed with him in this, but only to a certain extent, for Paul's thesis will then be that no one, neither Jew nor Gentile, is fully a doer of the Law, in which case circumcision is seen to be valueless.