The concept of "local church membership" hardly existed in the church before the 17th century Baptists, except for certain heretical sects and Anabaptists. Yes, the concept of "church membership" has existed from the very beginning. The concept of "local congregation" has existed from the very beginning. The theology of "there is no salvation outside the church" has existed from the very beginning; hence, the command for Christians to "join the church" in a covenant, which is the Covenant of Grace. That joining the Church, though, was done through the same means a man joined the Covenant of Grace: baptism. Through baptism, man joined the universal Church. The modern church, through a combination of political pressure and a move by church leaders to insulate themselves from accountability, has led to the widespread adoption of "local church membership" and related practices over the past century or so by non-Baptists as well. But this was not the way of the early church, Christendom, or the Reformation.