Everywhere Paul went false teachers followed him like yipping hyenas. They tried to say he was a lesser apostle, taught a different gospel, and now was at odds with the real apostles. He was too smart for them, but more importantly, too filled with grace. God redeemed him from murderous persecution and set him to work building the church more effectively than anyone. In these verses he teaches the Galatians about his trip to Jerusalem, the strength he showed against false brothers, and the unity of doctrine and mission that resulted.