Paul describes his first visit to the Corinthians.
When I came to you, brothers and sisters, I did not come with superior eloquence or wisdom as I proclaimed the testimony of God. For I decided to be concerned about nothing among you except Jesus Christ, and him crucified. And I was with you in weakness and in fear and with much trembling. My conversation and my preaching were not with persuasive words of wisdom, but with a demonstration of the Spirit and of power, so that your faith would not be based on human wisdom but on the power of God.
There isn’t much doubt Paul is referring to rhetoric when he talks of the absence of “persuasive words of wisdom” and “superior eloquence” in his speech. Paul believed using powers of human persuasion would empty the gospel message of its power.
For Christ did not send me to baptize but to proclaim the gospel, and not with eloquent wisdom, so that the cross of Christ might not be emptied of its power.
(1Co 1:17 NRSV)
Paul believed that the gospel message was powerful all on its own and didn’t need to be augmented through powerful tools of persuasion. He was confident that the gospel was like a key to unlock the human heart. We don’t have to force it or add to it. We just need to share it plainly because it’s powerful all on its own.
For the message about the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God.
(1Co 1:18 NRSV)
While it does seem clear that Paul was very apprehensive about leverage the human tools of persuasion in the spoken word he used rhetoric when composing his letters.
Ben Witherington wrote a series of commentaries where he delves in various gospels and epistles and analyzes their content according to the rules of rhetoric. Some letters, like many of Paul’s, reflect the guiding principles of rhetoric. It does present something of puzzle because even Mr. Witherington concludes that Paul avoided using at least some rhetorical tools when he came to Corinth.
In 2:1 logos would seem to refer to the form of the message and sophia to its content. Paul is repudiating using either the form or substance of a wisdom that might be called “worldly” in his preaching of the gospel. This might mean that he used rhetoric not in his preaching but in his letters, but more likely it means that he did not use ornamental or Sophistic rhetoric lest he distract the audience from the real power of the gospel message.
There are different kinds of rhetorical tools and some are manipulative to the point of being dishonest and others are not. I believe Paul was willing to use the approaches he deemed honest in his letters and refused to use it in speech, especially when proclaiming the gospel. Paul appears to concede to the Corinthians that the strength of his rhetorical power was much better displayed in his letters than his speech (1Cor 10:10) and that he just wasn’t a very good speaker (2Cor 11:16).
Paul was most likely being criticized by the Corinthians for his lack of rhetorical power. He admits in his first letter that he lacked strength in the three main components of rhetoric.
 Witherington, B., III. (1995). Conflict and Community in Corinth: A Socio-Rhetorical Commentary on 1 and 2 Corinthians (123). Grand Rapids, MI: Wm. B. Eerdmans Publishing Co.