The “church” in the aggregate, or in the “universal sense,” consists of all followers of God in Christ. It is the body of the saints, likened in a figure to a physical body of which Christ is the head (Eph. 1:22-23). One becomes a “member” of that body when “by one Spirit are we all baptized into one body”...and are “made to drink into one Spirit” (1 Cor. 12:13). That which puts one into Christ (Rom. 6:3; Gal. 3:27) makes one a member of the aggregate body of those who have come into Christ, therefore a member of His church. We might add that whatever takes one out of this relationship, takes one out of His church. (See Rom. 11:17-23; Rev. 2:4-5)
But “church” is also used with reference to groups of saints, that function as a unit or “team” (Phil. 4:15), having “overseers” and “servants” (1:1). This unit can hear and speak (Matt. 18:17); write letters (1 Cor. 16:3); choose and send messengers (2 Cor. 8:19); discipline (1 Cor. 5:5); etc. Now, what can put on in, or take one out of this relationship? Ideally, it is a local working group of exactly the same kind of people who make up the body of saints in the aggregate. One could become a member only by the process that puts one into Christ, and would no longer be considered a member if unfaithful to Christ. But the local church comes short of this ideal, and must by his nature. It is less than ideal because the human element enters into this “roll” taking.
The Corinthian church maintained fellowship (accepted as a “member”) one who was unfaithful to the Lord. They were sharply condemned for this, and told “he that hath done this deed” should be “taken away from among you” (1 Cor. 5:1-f). Turning the picture around, in 3 John we read of a church which “cast out” (no longer accepted as “members”) those who sought to do as the Apostle John directed. From this it is clear that “membership” in a local church rests upon fallible human judgment. The Apostle Paul was rejected by the Jerusalem disciples until Barnabas convinced them he was indeed a true saint (Acts 9:26-28).
It was wrong—to keep fellowship with the incestuous man, to “cast out of the church” those who sought to do John’s bidding—it was not according to the ideal—but they did it anyhow. And the same sort of errors exist today in the local churches.
A local church of Christ consists of those who judge one another to be followers of God in Christ; who have therefore covenanted together, tacitly if not expressly, to function as a team in that which they believe to be divinely authorized church worship and work. Strictly speaking they are “of Christ” to the extent that their faith and practice is true to Him.
Local church membership is indicative of one’s agreement to such fellowship, and acceptance by the same. It imposes “team” obligations, not the least of which is to maintain “team” faithfulness to Christ. Our first loyalty must be to Christ, hence we never lose individual responsibility.