In Vintage Church chapter nine we answer the question, "What Is a Missional Church?" With the ongoing debate between traditional churches, seeker churches, emerging churches, etc., there is a need to clarify what a missional church is and is not. In this chapter we explore the history and nature of a missional church. Regarding the missional church, excerpts from Vintage Church pages 219-220 say:
Thankfully, the mission of the church is not that complicated. The mission of the church comes directly from the command of Jesus, who, following his resurrection and just prior to his ascension, said, "Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age" (Matt. 28:19-20; see also Mark 16:15-16; Luke 24:46-49; John 20:20-31; Acts 1:5-8). Jesus speaks of going, evangelizing, making disciples, and planting churches that plant churches to continue the process. Therefore, the mission of the church is nothing less than bringing the entire world to Christian faith and maturity.
A missional church must strategize how to carry out the mission to today's increasingly non-Christian culture.
Still the best short piece I know of is What Is a Gospel-Centered Missional Church and Why Do We Need One? from The Journey Church (St. Louis). Read it all, but here's an excerpt:
Primarily, a missional church recognizes the centrality of the Gospel as its people live out the calling to be "for" the culture. This means a church must derive its purpose from the Gospel (1 Corinthians 15:1-4); it must be a servant of the Gospel that glorifies God by telling people the story of Jesus through word and action (1 John 3:16-17). A Gospel-centered church's ministry cannot be separated from the person of Jesus, nor can its mission be defined or performed apart from the Gospel. The Gospel is the ultimate guide and authority for how we function and minister as a church. Said another way, a missional church embraces God's call to be a sender of missionaries to its own culture (Matthew. 4:19; Acts 16:20; 17:6).
Again, read the whole thing.
Finally, this is from a piece I wrote back in my days at SearchWarp called The Meaning of Missional:
God is a missionary.
Throughout the great narrative of Scripture, what we see is God's initiative and man's response. This really does affect the way one thinks about worship and goes about worshiping. And it really does affect the way the community of Jesus followers thinks about discipleship and goes about discipling.
So for our community, "missional" means following God outside the church walls and into the warp and woof of human existence. It means echoing the emptying, sacrificing, and servanthood of the incarnation (God becoming man in Jesus) in our day to day walk. And to be a missional church means teaching people how to do this and actually doing it together.
Three angles, all complementary, I think.