I Corinthians 2:1-5 (ESV)
And I, when I came to you, brothers, did not come proclaiming to you the testimony of God with lofty speech or wisdom. For I decided to know nothing among you except Jesus Christ and him crucified. And I was with you in weakness and in fear and much trembling, and my speech and my message were not in plausible words of wisdom, but in demonstration of the Spirit and of power, that your faith might not rest in the wisdom of men but in the power of God.
I thought the following comments from Gordon Fee to be a helpful reminder as a pastor prepares to preach:
This paragraph has had an interesting history of application in the church, depending on where the emphasis has been placed. Some emphasize what Paul did not do, that is, preach with excellence of word and wisdom, and glory in a more rough-hewn presentation (which, interestingly enough, is often accompanied by a kind of bombast that seems intent on persuasion of a rhetorical kind, despite its protests to the contrary). Others wish to emphasize the "positive," the "proofs" of the Spirit's power, which they see as in contrast to mere preaching. On the other hand, the polished oratory sometimes heard in American pulpits, where the sermon itself seems to be the goal of what is said, makes one wonder whether the text has been heard at all. Paul's own point needs a fresh hearing. What he is rejecting is not preaching, not even persuasive preaching; rather, it is the real danger in all preaching--self-reliance. The danger always lies in letting the form and content get in the way of what should be the single concern: the gospel proclaimed through human weakness but accompanied by the powerful work of the Spirit so that lives are changed through a divine-human encounter. That is hard to teach in a course in homiletics, but it still stands as the true need in genuinely Christian preaching (Gordon Fee, The First Epistle to the Corinthians, NICNT (Grand Rapids: Eerdmans 1987), 96-97).