What Is a Church? The Who.
So, who makes up a church?
Interestingly, the use of the Greek word for church (ekklesia) as an intentional assembly is not the only way the word was used in the New Testament. There are two additional ways the word was used that flow out of the primary meaning.
First, the word ekklesia is sometimes used to describe the people who assemble or gather. Ferguson describes it this way:
It was natural to use ekklesia for the people, whether assembled or not. The great majority of instances of the word are in reference to a local church, hence the use of the plural for churches in a given region (1 Cor. 16:1, 9; Gal. 1:2, 22; Acts 15:41; 16:4-5). The use of the word for the people who customarily assemble, but whether assembled or not, shows that it had become a technical term.
So, “a church” also describes “those who assemble” as a church. In this sense, the word “church” is referring to the collective people. Here are some examples:
“To the church of God in Corinth, to those sanctified in Christ Jesus and called to be his holy people, together with all those everywhere who call on the name of our Lord Jesus Christ—their Lord and ours.” (1 Cor. 1:2)
“Great fear seized the whole church and all who heard about these events.” (Acts 5:11)
“On that day a great persecution broke out against the church in Jerusalem, and all except the apostles were scattered throughout Judea and Samaria.” (Acts 8:1)
“To the church of God in Corinth, to those sanctified in Christ Jesus and called to be his holy people…”
These passages describe the people—the ones who regularly and intentionally gather as a body—in a particular area.
Second, there is another important secondary use beyond the local assembly of Christians and those who assemble. The word ekklesia is also a word used for everyone in the world who comes together in all the Christian assemblies or gatherings. This is the universal church. Sometimes this is referred to as the “big-C Church,” whereas a local gathering is a “little-C church.” Again, Ferguson helps us:
Less frequently, ekklesia is used in a universal sense for all believers….The idea of assembly is not lost even in the extension of the word to the universal people of God, for in the background is the eschatological (end times) assembly of all the saved, which is described by different but kindred expressions (2 Thes. 2:1; Matt. 24:31)….There will be a time when the universal church is in assembly, when the Lord comes again. That eschatological “Day” gives urgency to the earthly meetings together of Christians (Heb. 10:25).
“Less frequently, ekklesia is used in a universal sense for all believers.”
Here are some examples of passages that talk about the universal church (big-C Church)—meaning the universal people of God:
“And I tell you that you are Peter, and on this rock I will build my church, and the gates of Hades will not overcome it.” (Matt. 16:18)
“God placed all things under his [Jesus’] feet and appointed him to be head over everything for the church, which is his body, the fullness of him who fills everything in every way.” (Eph. 1:22-23)
“And he is the head of the body, the church; he is the beginning and the firstborn from among the dead, so that in everything he might have the supremacy.” (Col. 1:18)
In this third sense, the church is a huge body of people—composed of those from all over the world—yet each person’s first identity is found locally, in a local assembly or church.
“…the church, which is his body, the fullness of him who fills everything in every way…”
It’s important to note how these descriptions of the church as a group of people specifies them as more than just a group of people who gather. These are people who are being sanctified (made holy) in Christ and who call upon his name (1 Cor. 1:2). These are people who actively live as Christ’s body—the extension of his presence on earth (Eph. 1:22-23). These are people who live as if Christ is their king, supreme over everything (Col. 1:18).
A previous article made us question whether someone can be part of a church if they don’t regularly assemble with other church people. Likewise, this article makes us question whether someone is part of a church if they take no intentional steps to be the type of people described in these passages—even if they do regularly gather together.
 Everett Ferguson. The Church of Christ: A Biblical Ecclesiology for Today (Kindle Locations 1755-1758). William B. Eerdmans. 1996.Kindle Edition.
 Everett Ferguson. The Church of Christ: A Biblical Ecclesiology for Today (Kindle Locations 1759-1764). William B. Eerdmans. 1996.Kindle Edition.