Albert Barnes Commentary Acts 18:9

"And the Lord said unto Paul in the night by a vision, Be not afraid, but speak and hold not thy peace:" — Acts 18:9 (ASV)

By a vision. See Barnes on Acts 9:10 and Acts 16:9.

Be not afraid. Perhaps Paul might have been intimidated by the learning, refinement, and splendor of Corinth; perhaps embarrassed in view of his duty of addressing the rich, the polite, and the great. To this he may allude in 1 Corinthians 2:3: And I was with you in weakness, and in fear, and in much trembling. In such circumstances, it pleased God to meet him and disarm his fears. This he did by assuring him of success. The fact that God had much people in that city, Acts 18:10, was employed to remove his apprehensions. The prospect of success in the ministry, and the certainty of the presence of God, will take away the fear of the rich, the learned, and the great.

Hold not thy peace; that is, "Be not silent."