Last time I talked about what the church is. There's a difference between the big-C universal body of believers in Christ, to use the common analogy, and the little-c local church. There is a difference between the two, which I'll get to, but as a general rule the local church has the same mission and purpose of the Church writ large.
But what is that mission? This question divides churches almost as often as does the question of what carpet to install in the sanctuary, or what color to paint the kindergarten room. It's an important one, and in answering the "mega" question, needs to be addressed. The Church's/church's mission is the foundation on what the rest of the series will tackle.
A mission, or purpose, is what gives an organization its reason to exist. It answers the "why" much as my first post answered the "who." It is often cast in terms of vision (i.e., what we see ourselves becoming) or mission statements. Many businesses use such statements to focus employee efforts, and set themselves apart in the minds of the community or marketplace. Teams will work long hours to define the "why" question for organizations of all stripes.
For the church, though, the mission has been defined for us. Jesus Himself gave it to us when He returned to Heaven. The mission of the church, quite simply, is to make disciples. This Great Commission is what Jesus left us on earth to do.
English translations often make the Great Commission look like we have a multi-part mission: go, make disciples, baptize, teach. This is slightly misleading, though, as the focus of the Greek is specifically on "going, and making disciples."* The real sense of the Great Commission is, to paraphrase, "go and make disciples by baptizing and teaching." It isn't to "go, make disciples, baptize and teach." It's a minor distinction, but it's important because there are some who believe the mission of the chuch can be subdivided into four categories, and we are fulfilling it if we are only teaching (or being taught.) Or if we are baptizing those who come to us, but we don't "go" to reach others. That is, some act as though the Great Commission isn't about leaving our comfort zones and reaching out to people who have yet to become disciples.
There are those who may argue that the mission of the church can be expanded to include helping the poor, or to corporate worship. One might say the church is for fellowship and communal learning or growth. And these are certainly good things, things which churches should do. But they are not the mission of the Church. If all church was meant for was fellowship, say, God would call us to Heaven as soon as we believed in Jesus. We could have all the fellowship we need there.
No, we are left here as representatives of God's kingdom explicitly to go and make disciples. Everything else (baptizing, teaching, fellowship, service, giving) is a part of disciple making. They are the "how" and the "what" - but not the "why." This does not make these things unimportant. That would be like saying the mission of the baseball team is to score runs, but practice and strategy don't matter. The "how" and "what" are vital questions, and to those we turn next.
The mission of the church, the "why" we are here: because Jesus gave us the job of going forth to make disciples. That is why the Church, and why churches, exist.
*Yes, I realize the Greek is such that some say the only verb is "make disciples." I think the Wallace quote on the post I linked to addresses that sufficiently that I hold the two-verb view. More here.