It’s obvious that the early church knew its flock well. In Acts 20, Paul exhorted the elders of the Ephesian church to faithfully watch over and shepherd their people. But it’s very difficult to shepherd if you don’t know who your flock is. And sheep don’t survive well just roaming around on their own.
While the New Testament never speaks of church membership in today’s terms, the principles of life in the early church lay the foundation for faithfully submitting and belonging to a local congregation. While the original membership process might vary from today’s patterns, there’s no doubt that New Testament Christians were lovingly united and bound to their local body of believers.