1 Corinthians 2:4 (ESV)

4 and my speech and my message were not in plausible words of wisdom, but in demonstration of the Spirit and of power,

Instead of human wisdom, Paul presented proof (demonstration) of the presence of God’s Spirit and power. This proof lay in the signs and wonders that Paul performed among the Gentiles (see Romans 15:18–19). Signs and wonders were a sign of apostleship (2 Corinthians 12:12).