Ephesus was one of the “epicenters” of Paul’s church planting ministry. While he taught in the lecture hall of Tyrannus for two years, people from all over the region of Asia came to be discipled by him. They, in turn, went back to their hometowns and started churches. In a sense, these churches were Paul’s spiritual grandchildren.
The letter to the Ephesians is actually a letter that was designed to be distributed to all the “grandchildren” churches in the region in Asia. That is why it has less of a personal flavor than most of Paul’s other letters.