At the time Paul wrote this letter, Christians were persecuted mainly by the Jewish community (who resented the inclusion of Gentiles). The Judaistic version of Christianity (forcing Gentile converts to become Jews) effectively reduced it to no more than a sect within Judaism, and thus made it more acceptable. So the Judaisers were not really motivated by zeal for God and His Law, but by self-interest (verse 12).
It is a perennial temptation for the Church to soft-pedal the message of the cross and replace it with a ‘safer’ religion – a religion of externals. For it is much easier to perform a ritual than to change one’s heart. The other problem with rituals is that they can all too easily be corrupted into a means of impressing other people. But a true Christian does not place any reliance on performance, or on any of the other stuff (e.g. holy objects, pilgrimages) that ‘tick all the right boxes’ for worldly religion. It is worldly religion that lays undue emphasis on external things – such as the mode of baptism, and other distinguishing marks between denominations. When the sign becomes more important than what it is supposed to represent, then something has gone seriously wrong.
Paul’s values had undergone a complete reversal, and were no longer the values of the world. His pride was not in anything that he had done, but in what Christ had done for him. “May I never boast except in the cross of our Lord Jesus Christ.” (verse 14) To join Christ means joining Him on the road to the cross – where people laugh, jeer and spit at you. But if we are truly committed to following Jesus, then what the world thinks will no longer matter to us very much. All the old symbols (the kind of thing that the world considers important) have become irrelevant; God’s people are now recognised by the inner transformation that comes from the Holy Spirit – the new creation (verse 15). “It is we who are ‘the circumcision’, we who serve God by His Spirit, who boast in Christ Jesus, and who put no confidence in the flesh.” (Philippians 3:3) The Church must never forget this…