What does Acts 18:9 mean?

This is a significant change in Paul's ministry. Although he spent years in his home base of Syrian Antioch, his missionary trips have been very transient. Luke doesn't tell us how long he spends at each city, but it's certainly no more than a few months.

Now, he is in Corinth, a pagan city known for pervasive sexual sin. So pervasive, in fact, that a Greek term for fornication, korinthiazomai, is derived from the name of the city. Paul has left the synagogue—and the protection of Judaism—and is meeting next door at the home of a Gentile who had attended the synagogue and now follows Jesus (Acts 18:6–7). Typically, by this point, the Jews in the synagogue would be convincing the prominent Gentiles of the city to force Paul out—or worse.

This time, however, God wants Paul to stay for a while. The people of the church in Corinth will need a lot of guidance. After Paul spends eighteen months establishing the church, Apollos will come and build on Paul's foundation (Acts 18:10–11; 1 Corinthians 3:6, 10). Paul will write four letters to the Corinthians, two of which we have as part of preserved Scripture. They show the Jesus-followers need significant help learning how to live godly lives.

Jesus appears to Paul in visions several times during his ministry. First at his conversion on the road to Damascus (Acts 9:5), then when he returns to Jerusalem (Acts 22:17–18). In Troas, Paul has a vision telling him to go to Macedonia (Acts 16:9). After his arrest in Jerusalem, Jesus will reassure him that he will go to Rome (Acts 23:11). We should not expect the same type of interaction with Jesus that Paul experienced. The beginning years of the church, as the message of Jesus' offer of forgiveness spread, required a lot of direct guidance. Now, God primarily speaks to us through the Bible.