Answer: From the start, I should clarify the intent of this question. In our church, we ask people to take vows, affirming that they believe the basic tenants of the Christian faith, and promising that they will endeavour to follow Jesus Christ. We have them meet with the elders to be interviewed, and to determine if they meet the requirements of membership.
There are times when this process has enabled us to pinpoint error in the candidate’s profession, either in belief or practice, and to help them come to a more credible profession of faith. For example, it was discovered that one prospective member had a deficient understanding of the plenary verbal inspiration of the scriptures. He was refused membership, but given some material to study and soon this deficiency was rectified and he was able to join. On another occasion, a prospective member was willing to accept God’s commandment for her own life, but was not willing to say that the standard applied to everyone. After a time, she also was able to work through this and be received upon a clear profession of faith and commitment to Jesus as Lord.
But it is readily admitted that these deficiencies could be corrected without a formal membership process. The real question that must be asked is: “what warrant do we have to impose formal membership upon the disciples of Jesus Christ as a requirement for participating in the Lord’s Supper with us?”
The warrant for covenant membership is found throughout the scripture. When God first brought Israel out of Egypt , He gathered them (into the church or assembly) and had them enter into a covenant, affirming their allegiance to him as His people and professing Him to be their God and Redeemer. This was a formal process—they entered into a covenant, making promises and taking vows.
Furthermore, from the beginning, the Lord recognised elders among the people. Very often, He met with the elders (a presbytery meeting) and then instructed them in what to say to the people. This is even the pattern in Egypt and at the Passover (Exodus 12), but even more so when it is formalised in the wilderness. These elders are to give instruction and oversight to the people, and they are responsible for certain members within the congregation. When strangers come into the community, they are not permitted to partake of the Passover (the covenant meal) until they have entered into the covenant by the sign of circumcision. And entering that covenant required them profess the Lord as their God and to promise to keep His statutes and ordinances as His people.
After Israel settled in the land, the elders and Levites continued to give oversight of the people (or at least they were supposed to), and there is much said in the law about those who are to be cut off because of an unacceptable profession. It was the task of these leaders to oversee the admission of the new members and to remove those whose profession was no longer acceptable. In order to perform this function, there had to be a list or designation of those who were in the congregation and those who were outside. You were either in or out. There was a formal procession of admission and formal process of excommunication (or removal).
When we come into the New Testament, we find that the same pattern is continued. Once again, there are elders in the local community, together with ministers of the word (the Levites are replaced by the ministers of the word and sacrament) who act as overseers and rulers of the congregation. And once again, they do this in the local assemblies in each community, and they also sometimes meet together with all the elders in their city (a meeting of the presbyters) as in Acts 20 where the elders at Ephesus meet with Paul and receive instruction, or Acts 21 where the elders at Jerusalem (there were many congregations at Jerusalem at this time) all meet together to decide how Paul should conduct his ministry there. And there is also the assembly of the whole church in Acts 15 when the elders and ministers of the word and other brethren met together to determine how to handle the matter of the admission of the Gentiles with regard to circumcision.
As in the Old Testament, the elders are responsible for admitting persons into membership when they have a credible profession (which of course must be examined by them with questions such as “Do you believe?”) and dismissing them when they no longer have a credible profession of faith. Once again, there is a covenant involved as new members are asked to confess their faith in Jesus Christ and their commitment to follow Him before they can be admitted, and are to be cut off if they do not continue in faith and repentance. They enter into the covenant by baptism. That there is a list of those who are in and those who are out is clear from such passages as 1 Cor 5 where the NT assembly is linked with the OT assembly in the ongoing requirement to “Remove the wicked man from among you.” This is done by the whole congregation through the officers (officers are officials who are appointed to act for the whole assembly) who represent them. It is a formal process in which covenant breakers are removed, and as Jesus puts it in Matthew 18, are regarded as unbelievers.
For proper government to be exercised, members must be identified with a particular assembly (or congregation). That way, if they begin to neglect the assembly, the elders can enquire about it rather than just assuming that they are at the congregation across town. And because some assemblies are not sound, when members move from one assembly to another, it is important for the elders in the receiving congregation to examine the candidate and not assume a credible profession. It is not necessary for the candidate to be baptised again, but it is important for them re-affirm their faith and their commitment before they are admitted to the new congregation. The new elders are undertaking responsibility for their oversight, and they should not admit them until they are satisfied that their profession is sound.
Now as to the details of just how the process of an interview is to be conducted and such matters—this is not expressly dictated to us in scripture. Therefore, there is room for variation. But the essential elements ought to be there. There should be a formal commitment made and there should be some sort of examination of the candidate’s profession and there should be a clear distinction between who is “in” and who is “out.”