How did new believers fresh out of paganism survive and grow when Paul left them so quickly?

Les explains that Paul was not in any one place very long. The Jerusalem church prospered because the apostles stayed and continued Christ’s ministry among Jews in Israel. But where Paul established churches, it was often only a week or two; Antioch was a year and a half, Thessalonica only a couple of weeks. Les says he cannot understand how new believers fresh out of paganism made it except by the miraculous power of God, by which Christianity began permeating the whole Roman Empire. The Corinthians, though carnal, were still believers, and their pagan setting—the temple of Aphrodite with 1,000 priestesses descending into Corinth at night—shows why Scripture had to be explicit about their bodies being members of Christ.