Acts 18:9 (ESV) … “And the Lord said to Paul one night in a vision, “Do not be afraid, but go on speaking and do not be silent…”
The Lord Comes to Paul (18:9a)
“And the Lord said to Paul one night in a vision…”
From time to time Paul received visions, given to him by God to strengthen, assure, and encourage him. He received such a vision at Troas, another after he was arrested in Jerusalem (23:11), and yet another that he described later to this same (by then) boastful Corinthian church, a vision none of them could hope to match, the kind of vision God gives, indeed, to very few (2 Cor. 12:1–5).
By now Paul was feeling the pressure in Corinth. Everywhere he had been, so far, the Jews had fomented trouble against him. It could not be long before the same thing would happen at Corinth and, after all, Paul was only human. He did not like being manhandled, maligned, imprisoned, beaten, or threatened any more than anyone else. The Lord, touched as He is “with the feeling of our infirmities” (Heb. 4:15), came at this juncture to his faithful ambassador and servant.
The Lord Commissioned Paul (18:9b)
Do not be afraid, but go on speaking and do not be silent.
It was just what Paul needed. As Jonathan once came to David to strengthen his hand in God, so the Lord came to Paul to encourage him to keep up the good work. Paul was a brave man in any case, but with this commission ringing in his soul he would be bolder still. He was brave but not reckless, bold but not brash, fearless but not fatalistic. What a happy balance we observe in this intrepid missionary, a man always conscious of the Lord’s abiding presence and daily leading. Paul’s fears were natural enough, but needless. He could write later to the Romans, “If God be for us, who can be against us?” (Rom. 8:31). Nobody was going to drive him out of Corinth. Here, for the foreseeable future, was where God wanted him to be. 
We must understand that whom the Lord calls, He equips and cares for. If God has called you to his service or to a particular ministry in life, God will not leave us without His care. We too can expect the Lord to speak to us His word of encouragement and His word of strength.