During the days of the early church, each local assembly was defined by geographic boundaries. There was the church of Rome, the church of Corinth, the church of Philippi, etc. Every believer living within those geographical areas would have been expected to participate in the fellowship of the one church, unlike today, where someone gets upset with the leadership at one assembly so he simply moves to another assembly. This is not apostolic. This is why on the one hand Acts 14:23 says, 'They had appointed elders in every church.' Yet Titus 1:5 says, 'Appoint elders in every city.' One city, one church. Not numerous autonomous churches in one city each with its own pastor, but one church led by one team of pastors/elders/bishops.