John6809 has answered this very adequately, I am sure. I would point out further (on a point to which he already alluded) that the people of Paul's day who accepted his claims were not men inclined toward "simple belief," but were people who not only expressed great initial skepticism about Paul, but also who might have a great deal at stake in accepting his claims without convincing proofs. He had been a persecutor, and a great danger to the Christian body. Suspicion that he was perpetrating a ruse in order to gain the confidence of the fellowship would be natural.But as for your method, John - do you engage Sufi and/or Hindi mystics with the same credulousness that you afford Saul of Tarsus?
Besides this, he was now claiming an authority equivalent to that of the other apostles—a claim we might expect to meet with strong resistance from the others . However, they became convinced of his genuineness by observing his miracles, his godly integrity and his willingness to suffer for his testimony. These were, apparently, very compelling evidences. Compelling enough, at least, to convince persons who had more at stake than we have in accepting Paul on his own terms.