Why did the Judaizers and Jewish leaders oppose Paul's message of grace to the Gentiles?
The Judaizers and Jewish leaders opposed Paul because he taught grace to Gentiles without requiring circumcision or Law-keeping. They insisted Gentile believers must be circumcised and keep the Law, and tried to convince Paul to add those requirements. Paul adamantly refused.
Les explains that the Judaizers and Jewish leaders—including Peter and the eleven—were coming down hard on the Apostle Paul for teaching his message of grace to the Gentiles. As earlier in Galatians, they tried to convince him that the Gentile believers had to practice circumcision and keep the Law. Paul adamantly refused. Later in chapter 15, Peter wakes up, realizing God had used him years earlier in Caesarea to take the Word to Cornelius, a Gentile, and Peter witnessed that Gentile’s salvation. Peter then asks why test God by putting a yoke on the neck of the disciples—meaning the believers in Antioch, who had become believers of Paul’s Gospel and were not under Law or legalism, but which the Judaizers were trying to put there.