Paul's Vindication of His Apostleship

Paul realized that he was singling out himself and his gospel when he condemned anyone and everyone who differed from the message he was proclaiming. And by insisting that he obtained his gospel without any input from the other apostles, he was allowing room for the charge that he had innovated his own message alongside - and perhaps even in contradiction of - the gospel being proclaimed by Jesus' other representatives. He could expect that this charge was being leveled against him by those who were "troubling" the Galatian believers and challenging his gospel. And so Paul knew that he needed to show that the other apostles affirmed both his apostleship and his message. If he couldn't, then he had no right to make the claims he was making.