“But when Cephas came to Antioch, I opposed him to his face, because he stood condemned.” —Galatians 1:11
Paul has already delivered a powerful one-two punch defending his apostleship and the gospel, now he finishes with a vicious uppercut. First comes the left jab in 1:10–24 where Paul demonstrates that his gospel did not come from or through men but through Christ. Paul didn’t get his gospel from Jerusalem to distort it. Second, Paul follows with the right cross of 2:1–10 showing the unity of the apostolic gospel. Paul took his gospel to Jerusalem where they recognized it. Now, in 2:11–16 he finishes with a strong uppercut for the KO. Here, Paul demonstrates that his apostolic authority stands even over another apostle when their conduct is contrary to the gospel.
Paul isn’t throwing Peter under the bus out of envy to establish that he’s the better apostle. The point in this isn’t the supremacy of Paul over Peter, but the supremacy of the apostolic gospel even over those who are apostles.
That this is so is evident in that our text opens not by contrasting Paul with Peter, but Peter with Peter. The “but when Cephas” of v. 11 is first in contrast to the “and when… Cephas” of v. 9. The contrast is between Peter as an apostle of the gospel and Peter’s behavior as a sinner saved by grace. Luther comments, “The apostles were not superior to us in anything except in their apostolic office. We have the same gifts they had, namely, the same Christ, Baptism, Word, and forgiveness of sins. They needed all this no less than we do; they were sanctified and saved by all this just as we are.”
Paul has already placed himself under the same standard in 1:8. The gospel is supreme, I don’t care who you are. And by the gospel, Paul has centrally in mind justification by faith alone. It isn’t Peter that Paul knocks out here, but the damnable teaching of salvation by works of law rather than faith in Christ alone.