By a vision - Compare the notes on Acts 9:10; 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.