In another thread, PaulSceptic wrote:
"All the Calvinists books in the world can't save the one 'born out of due' season from the fact that he has nothing upon which to claim an apostleship but a vision of a light and a voice, and yet he calls the inner circle of the twelve (Peter, James, and John) nobodies who only 'seemed to be something' (Gal 2:6,9) and then takes another jab at them saying 'if a man think himself to be something, when he is nothing, he deceiveth himself.' (Gal 6:3) Ok, so who is the nobody deceiving himself into thinking he is somebody? Paul who saw a light and heard a voice he didn't even recognize as Jesus' voice and had to ask 'Who are you Lord?' or Peter, James, and John, the inner circle of the twelve who alone got to see Jesus's glory on the mount of transfiguration (Mat 17:1-2), and see him raise Jairus' daughter from the dead (Mark 5:37), and who alone he took closest to him in Gethsemane the night in which he was betrayed (Mark 14:33)? Who's the nobody deceiving himself (not to mention his followers)? It ain't Peter. It ain't James. And sure ain't John. There's only one name left."
He assumes, without argument, that men like Peter and John are in view in Galatians 6:3. And he ignores the many places where Paul speaks positively of such men. He ignores the other evidence we have for Paul's apostleship.
Regarding the common claim that the apostles or the early Christians in general were significantly more disunited than Christians have traditionally believed, see here.