Peter erred in life and in doctrine. Paul might have dismissed Peter's error as a matter of no consequence. But Paul saw that Peter's error would lead to the damage of the whole Church unless it were corrected. Therefore he withstood Peter to his face. The Church, Peter, the apostles, angels from heaven, are not to be heard unless they teach the genuine Word of God.
A Commentary on St. Paul's Epistle to the Galatians (ed. CCEL, 1972) - ISBN: 9781610251082