1 Corinthians 2:1
And I, brethren, when I came to you, came not with excellency of speech or of wisdom, declaring unto you the testimony of God.
Note 1 at 1Co 2:1: The Greek word that was translated "excellency" here is the word "HUPEROCHE," and it means "prominence, i.e. (figuratively) superiority (in rank or character)" (Strong's Concordance). Paul was saying that it wasn't his great speaking ability that persuaded the Corinthians to believe. He was not a superior speaker.
In fact, Paul quoted some of the contentious Corinthians as saying that his speech was contemptible (2Co 10:10). Apparently, Paul's physical stature and his speech were unimpressive, but what he lacked in the natural, he made up for in the supernatural.
Although Paul was very intelligent and had a great revelation of the things of God, he was not an exceptional speaker. Therefore, he was an example of God using the weak things of the world that he had just described in 1Co 1:27-29. Paul was as successful as anyone has ever been in bringing people to salvation in Christ. But it wasn't through excellent sermons; it was through the anointing of God.