The word "church" comes from the Greek term ekklesia which is formed from two Greek words meaning "an assembly" and "to call out" or "called out ones."
In summary, the New Testament church is a body of believers who have been called out from the world by God to live as his people under the authority of Jesus Christ (Ephesians 1:22-23). This group of believers or "the body of Christ" began in Acts 2 on the Day of Pentecost through the work of the Holy Spirit and will continue to be formed until the day of the rapture of the church.
Becoming a Member of the Church
A person becomes "a member" of the church simply by exercising faith in Jesus Christ as Lord and Savior.
The Church Local Versus the Church Universal
The local church is defined as a local assembly of believers or a congregation that meets together physically for worship, fellowship, teaching, prayer and encouragement in the faith (Hebrews 10:25). At the local church level, we are able to live in relationship with other believers—we break bread together (Communion), pray for each other, disciple, and strengthen one another.
At the same time, all believers are members of the universal church. The universal church is made up of every single person who has exercised faith in Jesus Christ for salvation, including members of every local church body throughout the earth (1 Corinthians 12:13; Ephesians 1:22-23).
So, Who is the Church?
The founder of the "home church" movement in England, Canon Ernest Southcott, said it best:
"The holiest moment of the church service is the moment when God’s people—strengthened by preaching and sacrament—go out of the church door into the world to be the church. We don’t go to church; we are the church."
The church, therefore, is not a place. It's not the building, it's not the location, and it's not the denomination. We—God's people who are in Christ Jesus—are the church.
The Purpose of the Church
The purpose of the church is two-fold. The church comes together (or assembles) for the purpose of bringing each member to spiritual maturity (Ephesians 4:13). The church reaches out (scatters) to spread the love of Christ and the gospel message to unbelievers in the world (Matthew 28:18-20). This is the Great Commission. So, the purpose of the church is to minister to believers and unbelievers.
The church, both in the universal and local sense, is important because it is one of the main vehicles through which God carries out his purposes on earth. The church is the body of Christ—his heart, his mouth, his hands and feet—reaching out to the world.