Today we look at to the sixth affirmation of The Missional Manifesto: Christocentricity. I want to encourage you to go back and read through the other posts written around the first five affirmations to get an idea of the flow of the document. You can find them here:
Here is the wording of the manifesto's sixth affirmation:
We believe that Jesus is the center of God's plan. By extension, the church as the body of Christ is the primary medium of God's mission to His world. We affirm that while God's work and presence is not limited to the church, nonetheless the proclamation of the gospel of Christ comes through the church and believers everywhere. Members of the church, living by the power of the Spirit, are being conformed into the likeness of Christ in their attitudes and actions.
It is very easy in the missional conversation to lose the forest for the trees. We talk about missional communities, missional churches, and even missional service to our cities, but we can easily sidestep and sometimes altogether forget that at the center of God's mission is Jesus. Through the person and work of Jesus, the mission of God is centralized.
Another way to say this is that neither the church nor the mission is the center of God's plan, Jesus is. But the church is central part of God's plan and the church's mission is the centripetal force in God's plan. God's mission blueprint to reach the world with the saving knowledge of Himself is the church, but we must be careful not to place the church at the nexus of the mission of God. That place is reserved only for Jesus Christ.
In my book, Breaking the Missional Code: When Churches Become a Missionary in their Community, I talk about this in another way that might be helpful:
Missiology is birthed from our understanding of who Jesus is. Jesus said, "As the Father has sent me, I am sending you" (John 20:21). Who Christ is and how he is sent matters. How we do mission flows from our understanding of God's mission and directs our missiology. How we do church is grounded in Scripture but applied in culture. Thus we have the intersection of who Jesus is and what he has sent us to do (Christology); the forms and strategies we use to to most effectively expand the kingdom where we are sent (missiology); and the expression of the New Testament church that is most appropriate in this context (ecclesiology). 
Out of this understanding, I developed something called "The Missional Matrix" (see below). Christology, missiology, and ecclesiology, rather than being a linear progression, find themselves in an ongoing conversation and interaction of theological disciplines.
"The Missional Matrix" begins with the necessity of the scriptural and theological foundation and its Spirit-enabled application. When a church or movement goes beyond this foundation, they will become unbalanced and outside of the bounds of Scripture. The following are a few examples of what happens when a movement becomes unbalanced.
The church growth movement, most friends and critics would agree, was probably weakest in its understanding the nature of the church as an extension of Christology. The result was an anthropocentric (or more man-centered) emphasis on tools and techniques, or methodology, straying slightly outside of a scriptural foundation and application.
Just as the church growth movement was too man-centered, the church health movement was too church/body focused. This movement was centered on how the church body was related to Christ (Christology), as well as what form of church was best (ecclesiology). Unfortunately, this inward focus can result in blindness to the community, other races, and other contextualized approaches to church, thus making a church less missional.
Of course, an emphasis on missiology and Christology without a proper emphasis on ecclesiology leads to a focus on being sent to the culture without an understanding of biblical teaching on the church. When the church steps out of the scriptural and theological bounds in this situation, the result is syncretism - mixing up the gospel with the world in such a way that you can't tell the difference.
This affirmation goes on to say:
By extension, the church as the body of Christ is the primary medium of God's mission to His world. We affirm that while God's work and presence is not limited to the church, nonetheless the proclamation of the gospel of Christ comes through the church and believers everywhere.
Here again we see that God's divine missionary activity includes the Father, Son, and Holy Spirit sending the church into the world. Mission is therefore God's work in the world; the church is viewed as an instrument for that mission. As I've said before, there is a church because there is a mission, not vice versa.
In the book of Matthew, we see a beautiful picture of how Christology impacts our missiology and ecclesiology when Jesus gives the keys of the kingdom to his disciples. In this passage, Jesus is announcing that the church is birthed in the wake of the Kingdom - He is Messiah. He is announcing that he is the cornerstone of the church and that Peter's confession is the founding of the church. And finally, when Jesus says, "I will give you the keys of the kingdom of heaven," he is announcing that the church (represented here by Peter) holds the keys to the Kingdom. The church and the Kingdom are inseparable, but there is a distinction between the two.
Keys and doors are always connected. People enter through "doors" that are opened with "keys." In this case, the church holds the keys, and the door opens into the Kingdom. The "door" of the Kingdom is unlocked through proclaiming the good news. So, entrance into the kingdom of God is made possible by the keys held by the church. With the arrival of and accomplished work of Jesus the Messiah, the Kingdom arrives and the church is built.
 Ed Stetzer and David Putman, Breaking the Missional Code: When Churches Become a Missionary in their Community (Nashville, TN: B&H Academic, 2006), 53.