The following is an excerpt from The MacArthur New Testament Commentary on Acts 18.

And the Lord said to Paul in the night by a vision, “Do not be afraid any longer, but go on speaking and do not be silent; for I am with you, and no man will attack you in order to harm you, for I have many people in this city.” And he settled there a year and six months, teaching the word of God among them. (18:9–11)

The Lord’s encouraging message, “Do not be afraid any longer, but go on speaking and do not be silent” answered the struggle in Paul’s mind. The supernatural vision provided four reasons for him not to give up proclaiming the gospel in that city. First, God commanded it specifically when He said “go on speaking.” Second, God reminded him, “I am with you.” He gave a similar revelation to Joshua when he assumed the leadership of Israel after Moses’ death:  No man will be able to stand before you all the days of your life. Just as I have been with Moses, I will be with you; I will not fail you or forsake you…. Have I not commanded you? Be strong and courageous! Do not tremble or be dismayed, for the Lord your God is with you wherever you go. (Josh. 1:5, 9)With the Lord’s powerful presence aiding his ministry, Paul could accomplish whatever God intended him to. The Lord stood by him until the very end of his ministry (2 Tim. 4:16–18) and promises His presence to all believers (Matt. 28:20; cf. Isa. 41:10; Jer. 1:17–19).

Third, God promised Paul that “no man will attack you in order to harm you.” Those under God’s protection are invulnerable (cf. Isa. 54:17; Rev. 11:5).

The final reason God gave Paul to keep preaching was that He had many people in this city. All those in Corinth who “had been appointed to eternal life” had not yet “believed” (Acts 13:48). The truth of election expressed in verse 10 balances the truth of human responsibility in verse 6. As always, Scripture presents those two inscrutable truths without attempting to harmonize them. Both are true, and there is no real contradiction between them. (For further discussion of this issue, see the exposition of Acts 13:46, 48 in chapter 3 of this volume.) Here it is clear that some people belong to the Lord who are not yet saved, and they will not be saved without the preaching of the gospel (cf. Rom. 10:13–15). Paul defined his preaching as having the purpose of bringing the elect to faith (cf. Titus 1:1).

His strength fully renewed by God’s promise to him, Paul settled in Corinth for another year and six months, teaching the word of God among them. He continued to minister in that strategic location, and the elect continued to be saved and grow in their faith. During that period a certain incident provided the final source of God’s encouragement to Paul.