Understanding the measurement of professing and affiliated believers brings in two related issues. If you have an estimate of the total number of “Christians” in a country (in the widest sense), then you can say the following:

Total Christians - Total Professing = Total Secret

and

Total Christians - Total Affiliated = Total Unaffiliated

When a person becomes a member of a church, they usually go through a process of membership. We can’t judge the condition of their hearts, so we tend to measure the quality of a person’s commitment to Christ by the quality of his commitment to the church, based in large part upon their “membership standing.”

In our church, this membership process is designed to accomplish several things. First, its intended to make sure the person is a believer in Christ (have they invited Christ into their heart? have they made Him Lord of their life? have they been baptized?).

Second, it’s intended to make sure they understand some basic essentials of citizenship: what the church believes on certain core elements of doctrine, how church community works in this context, etc.

Third, it helps the new member to understand how this particular congregation works. This is less a doctrinal thing and more a management thing - in our church, for example, we were told during our “Discovery” class that while the church believers in tongues and interpretation of tongues, we desire that these things be done in an orderly fashion, so only people who had been through a class on the gifts of the Spirit were generally invited to speak out during a service. (I’m not sure how this is “enforced” but it’s the general idea.)

So we go through this process of becoming a “member” of the church. We are then counted as part of the membership, and thus counted among those who are “affiliated.”

“Unaffiliated” happens when a person professes on a government census or a public opinion poll that they are a Christian, but they don’t attend a church. This situation crops up in large amounts in Westernized countries. There is large debate over whether these people are actually “Christians” or “true believers,” and I won’t get into that debate here. Johnstone in Operation World terms this condition “nominal Christianity”. Barrett in the first edition of the World Christian Encyclopedia did the same, but in the second edition calls it “unaffiliated.”

On the other hand, if someone were to LEAVE the church, they would become “disaffiliated.” This individual was once affiliated, but no longer. This is somewhat harder to measure, since few denominations keep statistics on the number of people leaving their congregations.

A further complication is that, in some instances, you have people who are members of two churches. They are on the rolls of one because they fulfilled their basic membership requirements (perhaps attendance once or twice a year, plus being baptized), and they have not left it but they no longer attend it on a regular basis (e.g. every Sunday). They might attend an entirely different church on a regular basis. (So, for example, you might be on the rolls in a Catholic church but be attending a Pentecostal Protestant church on a regular basis). This is “doubly-affiliated.”

These measures tell us quite a bit about the character of the church within a specific country. While they generally hint at the spiritual character of the church, however, we should not make the mistake of thinking they are a direct measure of its quality. They are diagnostic of the organization called “Christianity”, but not of the organism which is comprised of “those who follow Christ.” We should be careful that we understand the two as not being necessarily the same.