From my reading in Acts 18 in the One Year New Testament.
If God has given you a vision then it is your duty to carry it out diligently.
Jesus said some very encouraging things to Paul,
“One night the Lord spoke to Paul in a vision and told him, “Don’t be afraid! Speak out! Don’t be silent! For I am with you, and no one will attack and harm you, for many people in this city belong to me.” So Paul stayed there for the next year and a half, teaching the word of God.” Acts 18:9–11
Jesus encouraged Paul to speak out for him and promised He would be with him.
When God calls us he will go with us.
These instructions are specifically to Paul, but I do believe that if God has called you to a city then usually there are people there who belong to Him whom he wants you to try and reach.
The lesson I take away from this passage is that Paul obeyed.
He spent the next year and a half teaching the word.
If God calls you to do something, not matter how hard it is don’t give in to fear, don’t get discouraged, speak out, and obey God because he wants to use you.
You may never know all the lives you can touch simply by following the vision God has given you!