1 Corinthians 7:18,19

‘Was any man called being circumcised, let him not become uncircumcised. Has any been called in uncircumcision, let him not be circumcised. Circumcision is nothing, and uncircumcision is nothing, but the keeping of the commandments of God.'

Physical signs, or the lack of them, are nothing to God. If a man is circumcised he does not need to have an operation to show that he is no longer a Jew. Indeed as a Christian Jew he can continue witnessing to Jews, just as Paul does (1 Corinthians 9:20). If a man is uncircumcised it will not benefit him at all to become circumcised. God will not thereby look on him differently. Such outward things are irrelevant.

What matters in both cases is submission to the will of God demonstrated by keeping His commandments (see Romans 2:25), and these centre around ‘you shall love your neighbour as yourself' (Romans 13:9; Galatians 5:6; Galatians 5:14; James 2:8; Ephesians 6:2; 1 Timothy 1:5; 1 Timothy 6:11). The wide view we are to take of ‘commandments' is demonstrated in John's letter (1 John 2:3; 1 John 2:8; 1 John 3:23; 1 John 4:21). In the end what God looks for is obedience to Him and love for one another. This is the responsibility of every Christian, not in order to attain salvation, but because they have received salvation, because they have been ‘sanctified' and are God's dwellingplace..

Paul's declaration here was important. The Jews despised those who were uncircumcised, and the Greeks tended to despise those who were circumcised and had thus marred the perfect body. But God says that neither condition matters. What is relevant is that He can use each in the sphere in which he finds himself. The circumcised have the advantage when witnessing to the circumcised, the uncircumcised when witnessing to Gentiles. But elsewhere he will point out that circumcision, like the sacrificial system, has in fact come to fulfilment in the crucifixion of Christ. The shedding of blood in circumcision looked forward to His work on the cross, and those who come to benefit from His death are circumcised spiritually through union with Him in His death as a result of putting off the body of flesh, the old life and the old ways. The old physical rite is therefore done away, replaced by the spiritual, which is a sign of their death to sin and their new obedience (Colossians 2:11).