Peter had been entrusted with the gospel of the circumcision, while Paul had been given a ministry to the heathen. The leaders in Jerusalem recognized this distinction and agreed to limit their ministry to the circumcision while Paul continued among the uncircumcision.
Yet when Peter later came to Antioch to visit, he separated himself from the Gentile believers because he feared those who were of the circumcision. Paul withstands Peter because his actions were contrary to the truth of the gospel.