Paul spent a few days in Galatia, a few days in Philippi, a few weeks Thessalonica and a few days in Athens. Then he spent 18 months in Corinth. Now, as a kind of climax to his missionary work, he is in Ephesus.
Ephesus is a great city, a trade hub. It's full of culture, money and temples, politics, soldiers, merchants and slaves. And power. Not only was it a place of civic power but it was also a place of religious and spiritual power. It is no accident that Luke begins Paul’s time in Ephesus with an outpouring of the Holy Spirit. There must be nothing secondhand about the Holy Spirit’s power when you are faced with the powers of the world.