"In 'Christendom' you can afford to train people just in prayer, Bible study, evangelism--private world skills--because they are not facing radically non-Christian values in their public life--where they work, in their neighborhood, etc.
In a 'missional' church, the laity needs theological education to 'think Christianly' about everything and work with Christian distinctiveness. They need to know: a) what cultural practices are common grace and to be embraced, b) what practices are antithetical to the gospel and must be rejected, c) what practices can be adapted/revised.
In a 'missional' situation, lay people renewing and transforming the culture through working with Christian distinctiveness in their vocations must be lifted up as real 'kingdom work' and ministry along with the traditional ministry of the Word.
In Christendom, 'fellowship' is basically just a set of nurturing relationships, support and accountability. That is necessary, of course.
In a missional church, however, Christian community must go BEYOND that to embody a 'counter-culture', showing the world how RADICALLY DIFFERENT a Christian society is with regard to sex, money, and power.
1) In sex. We avoid the secular society's idolization of sex and traditional society's fear of sex. We also exhibit love rather than hostility or fear toward those whose sexual life-patters are different.
2) In money. We promote a radically generous commitment of time, money, relationships, and living space to social justice and the needs of the poor, the immigrant, the economically and physically weak.
3) In power. We are committed to power-sharing and relationship-building between races and classes that are alienated outside of the Body of Christ.
In general, a church must be more deeply and practically committed to deeds of compassion and social justice than traditional liberal churches and more deeply and practically committed to evangelism and conversion than traditional fundamentalist churches. This kind of church is profoundly 'counter-intuitive' to American observers. It breaks their ability to categorize (and dismiss) it as liberal or conservative. Only this kind of church has a chance in the non-Christian west."
...Tim Keller, The Missional Church, June 2001