10For I am with you, and no one is going to attack and harm you, because I have many people in this city."
11So Paul stayed for a year and a half, teaching them the word of God.
Don't Be Afraid
I am encouraged that even Paul was afraid at times about delivering the message of God. He struggled with negative emotions. There were obviously many factors as to what he feared, and we could speculate about all of them, one definite factor we can deduce from verse 10, is that Paul dreaded the inevitable mistreatment from the Jews.
Even strong men are afraid at times, but the reassurance of the Lord's message in the night was something that Paul could trust, so he stayed in Corinth for a year and a half.
God's protection of Paul was not simply to benefit Paul, but to benefit receptive souls in Corinth.