Concerning certitude and Paul:
For ye have heard of my conversation in time past in the Jews' religion, how that beyond measure I persecuted the church of God, and wasted it: And profited in the Jews' religion above many my equals in mine own nation, being more exceedingly zealous of the traditions of my fathers.
But when it pleased God, who separated me from my mother's womb, and called [me] by his grace, To reveal his Son in me, that I might preach him among the heathen; immediately I conferred not with flesh and blood: Neither went I up to Jerusalem to them which were apostles before me; but I went into Arabia, and returned again unto Damascus.
Then after three years I went up to Jerusalem to see Peter, and abode with him fifteen days. But other of the apostles saw I none, save James the Lord's brother. Galatians 1:11-19
So then neither is he that planteth any thing, neither he that watereth; but God that giveth the increase. I Cor 3:1-7
As Dr. Eckleburg quoted it:
To the contrary. The two (and St. peter included with St. James) did not historically get along as well. Thye represented two divergent branches of Christianity.