Why did Paul have to confront Peter to his face about walking not uprightly?
Peter was not walking uprightly according to the truth of the gospel—the gospel of grace. His conduct still reflected dietary rules and regulations that separated Jew and Gentile, and he was not yet ready to recognize that there is now no difference between Jew and Gentile.
Les explains that the issue was the truth of the gospel—Paul's gospel of grace, which sets us free from dietary rules and regulations. Since there is now no difference between Jew and Gentile, Peter's conduct was inconsistent with that message, and Peter was not yet ready to recognize it. Les also points to II Peter 3:15-16, written shortly before Peter and Paul were martyred, where Peter calls Paul 'our beloved brother' and acknowledges the wisdom given to him.
But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?
What is the "truth of the gospel" Paul says Peter was not walking uprightly according to in Galatians 2?
The truth of the gospel is Paul's gospel, the gospel of grace, which sets believers free from dietary rules and regulations. It declares there is now no difference between Jew and Gentile. Peter was not yet ready to recognize that, so he did not walk uprightly according to it.
Why did Paul have to confront Peter to his face in Antioch?
Peter, as an ordinary practicing Jew, yielded to a moment of weakness among Gentile believers and blew his testimony again. His withdrawal from eating with Gentiles led other Jews and even Barnabas into dissimulation and hypocrisy, so Paul had to call him on it.
More Questions
What is the 'truth of the gospel' in Galatians 2:14 that Peter was not walking according to?
The 'truth of the gospel' that Peter was not walking according to is Paul's gospel, the gospel of grace, which now sets believers free from dietary rules and regulations.
Why did Paul confront Peter in front of everyone in Galatians 2?
Paul publicly confronted Peter because Peter, Barnabas, and the other Jews were not walking uprightly according to the truth of the gospel.