Pay attention to this quote from "Understanding North American Culture" chapter two of Missional Church; this section written by Craig Van Gelder:
"Freely choosing, autonomous individuals, deciding out of rational self-interest to enter into a social contract in order to construct a progressive society, became the central ideology of modernity."
Read it again.
So much of so-called mainline and progressive church, including my own tribe of Unitarian Universalism on the far spectrum of that but squarely in the center of having created and shaped American spiritual landscape, fits that description to a tee. Our churches in the progressive and mainline mode are embedded in modernity. What happens when that is no longer the air around us in which we must breathe? We bottle what we can of it and subsist on it? But for how long? At what cost of cutting us off from the new air and lifeblood of new creation emerging around us.
Missional church is embedded in a different culture, though still navigating through the wreckage of modernity. In this postmodernity missional church finds its DNA not in Reformation and Renaissance and Enlightenment, but in the DNA of premodernity which shares more with the current and coming culture(s) of our context than does modernity. As a Christian I can say that the roots of my faith are back with the murky missional ways of the Jesus communities before and after 70 CE, and so though I am born once into modernity because of my age and location, I am born again, through the missional church, into deeper sense of relationship and inheritance and belonging with those earlier times, fully realizing that our call is not to go back there, because we can't and wouldn't want to go back to that home again. But it can nurture us and help us use the developments of the renaissance reformation and enlightenment without having to be used up by their ghost.
Until progressives become born again of a different source, missional will seem a far land they have been exiled from.
Progressives can, however, draw from our own church history to feel supported in missional work. Witness the Cambridge Platform of 1648. Two major things occurred in the creation of the founding document of American congregationalism that shaped our whole civil society as well as a few religious movements. The Puritans gathered and without ado adopted theologically the confessions of orthodoxy of Westminster; this in a way freed them to do the second thing, to be groundbreaking and experimental in adopting a new kind of polity and ecclesiology (new, but one that they were at pains to point out were rooted in the early church, and in the inspiration of the Hebrew scriptures). Of course you can't separate ecclesiology from the theological web and so that new polity over time and with other influences affected the original orthodoxy as well. So progressives have precedent at plunging into the waters of reforming ecclesiology.
The mainstays it seems of the missional church are doing a similar two-step dance today. They are saying we are not going to address theological confessions of orthodoxy and adherence on creeds which have given us our identity and connected us to many of our brothers and sisters in Christ; we are going to accept those and move on, and not get caught up in the cultural battles over role of women, for example, or gay and lesbian et al, but will focus on the reformation or at least extension of what it means to become the church. However, at the root of the missional worldview, is the primary context not of the church for itself but of the world as it is waiting for the service of the church to change itself so it can change the world and bend it back toward the lovingkindness and justice of God. Progressives have gifts of how to engage with all of the world, in all its pluralisms, that the non-progressive missionals need in order to better know and love the world and become the church in the process. Otherwise so much of the world to be missional within will be left behind. And part of that progressive gift is the gift of theological pluralism itself surely as much a challenge to missionals, as the challenge of postmodernity is for the progressive church that can only see itself as a church of modernity.
So, not freely choosing but Chosen; not autonomous but inherently and primarily relational and communal, and finding deeper definitions of freedom in that; not individuals but persons, with personhood possible only as a relational self that is formed in community; not entering into community out of rational self-interest but to give up ego and to give one's self to all that the culture of consumerism and self and nationalism says does not make sense; covenanting to imitate and in doing so help initiate the "empire of God" or beloved communitas, taking a central stance in the new context of postmodernity.