In granting the Christian church special favors and privileges in the fourth century, the Roman Emperor Constantine ushered in the era of the church-state partnership that would profoundly shape European society and culture for centuries to come. As the protected and privileged religion of society, Christianity achieved unrivaled cultural dominance. The resulting cultures in Europe and later in North America became known as Christendom. Even though the legal structures of Christendom were removed in North America (i.e., the separation from the state), the legacy of this Constantinian system remained by means of powerful traditions, attitudes and social structures that could be described as "functional Christendom."
In the age of Christendom, the church occupied a central and influential place in society and the Western world considered itself both formally and officially Christian. So when we speak of post-Christendom, we are making the point that the church no longer occupies this central place of social and cultural hegemony and Western civilization no longer considers itself to be formally or officially Christian.
This represents a monumental shift in the cultural context into which the Western, and specifically American, church is now attempting to carry out its mission. This raises two fundamental questions: What does this new cultural context mean for the church and its mission? And, what exactly is the church's mission?
To the first point, the vast majority of American churches still rest on the assumptions of Christendom, meaning they believe that Christianity still occupies a central and influential place in society, when this is no longer true. A brief survey of American culture should quickly and thoroughly convince anyone that Christianity is no longer the central informing influence. Every culture forming institution from academia, media, the Arts, business and government are today, convincingly secularized. Religion in general and Christianity in particular are excluded from the public square. Christianity has become a marginalized way of thinking that is largely relegated to the elderly and uneducated. In other words, Christianity is regarded as being irrelevant when it comes to having anything meaningful to offer relative to "non-religious" matters.
The prior reality of Christendom naturally produced what could be thought of as a church-centered or ecclesiocentric perspective of its mission. Since Christianity was the dominant religion, the emphasis or mission of the church gradually became centered on recruiting "members" through evangelism as its social and cultural authority was firmly established. But, I would argue that this neither fully represents the true mission of the Church as God's sent people. Furthermore it disregards the post-Christendom reality. Christendom inevitably led to a view of "missions" as a program of the church while its de facto mission remained centered on the institutional maintenance of the church.
In the Missional Church: A Vision for the Sending of the Church in North America, the authors offer critical insight into the problem. Written in response to research inaugurated by the Gospel and Our Culture Network, a diverse team of evangelical theologians writes:
We have come to see that mission is not merely an activity of the church. Rather, mission is the result of God's initiative, rooted in God's purposes to restore and heal creation. "Mission" means "sending," and it is the central biblical theme describing the purpose of God in human history…. We have begun to learn that the biblical message is more radical, more inclusive, more transforming than we have allowed it to be…. We have begun to see that the church of Jesus Christ is not the purpose or goal of the gospel, but rather its instrument and witness. God's mission embraces all of creation.