In Galatians 5 the apostle Paul says, And I, brethren, if I yet preach circumcision, why do I yet suffer persecution? then is the offence of the cross ceased.
Circumcision here is a reference to Jewish supremacy. The Judaizers were attempting to undermine the gospel which Paul had ministered to the Galatians and were attempting to make Jewish converts of them.
This same thing had happened at Antioch in Acts 15. There were certain men who came down from Judaea and taught the brethren that unless they were circumcised after the manner of Moses, they could not be saved. Paul and Barnabas vehemently withstood them. Later the Apostles and elders along the church at Jerusalem held a meeting to resolve the issue. They came to the conclusion that the Gentiles were not obligated to be circumcised and come under the Law of Moses.
The issue of circumcision in the first century church wasn’t merely about “legalistic works” as we in the church today would refer to legalism. It was much more than that. It literally meant being converted to Judaism and becoming a Jew. It was for this purpose that the Apostle Paul was being persecuted by those who preached circumcision. Paul preached that the cross alone could save and being circumcised or not being circumcised no longer had any meaning with regards to covenant with God.
To put it another way, being a Jew or not being a Jew no longer had any bearing on who was God’s people and who wasn’t. God had abolished the separating wall between Jews and Gentiles in the death and resurrection of Jesus. God’s people are no longer of one ethic group in the flesh, but rather are people of every nationality united in one new man, in one body of believers, in Christ Jesus. What matters now is being a new creature in Christ Jesus.