Charles Ellicott Commentary 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:" — 1 Corinthians 2:4 (ASV)

And my speech.—The result that necessarily followed from this weakness and trembling was that neither his “speech” (i.e., the style of his teaching) nor his “preaching” (i.e., the subject matter of his teaching) was of such a kind as to appeal to the natural tastes of the Corinthians.

Demonstration of the Spirit.—The Apostle’s demonstration of the truth of the gospel was the result of no human art or skill, but came from the Spirit and power of God, and therefore the Corinthians could glory in no human teacher, but only in the power of God, which was the true source of the success of the gospel among them.