1 Corinthians 2:4

And my speech and my preaching were not in persuasive words of wisdom, but in demonstration of the Spirit and of power.

Macknight's paraphrase of this is:

Paul's discourses were neither composed nor pronounced according to the rules of Greek rhetoric, yet they were accompanied with the powerful demonstration of the Spirit, who enabled him to prove the things he preached by miracles.[14]

Of course, there was a reason for Paul's renunciation of the methods of the rabble-rousers; and that reason he at once emphatically stated.