I believe that one of the reasons why some churches in America are ineffective and irrelevant is that we have let church forms and functions dictate our mission. God calls us to first be missionaries - not first define who we are and what we do (we're this type of people and we do these types of things), and then out of that; form our mission.
A lost message, lost doctrine, lost way of the Christian is that all Christians are missionaries. As soon as you believe, you are a missionary.
Most Christians in America go to church services a lot and go on missions a little. It should be the other way around.
You might be asking, "where does mission come from?" The answer is God. At the center of everything is God. In the beginning, God. God created man and man fell. Then God began to reveal his plan to redeem man, culminating in God's sending his only son on the mission that we read about in the four Gospel (good news) books. For God so loved the world that he sent his only Son.
God sent Jesus on a mission. Jesus, by The Spirit of God, sends Christians on his mission. New Christians are birthed within the mission work or context and form church. Can pre-Christians find Christ in the church gatherings or meetings? Of course. That's not my point. My point is that evangelism comes before church formation or that church formation comes from your evangelism. How your church looks will depend on who your church is. So your church can become any form, depending on the people. In many churches today, the form is set and then many people don't fit. That's backwards. It ought not be that way.