Thanks Tim Keller for your stimulating material. Here's an extract from his latest e-newsletter- The Movement -- worth subscribing to.

The Necessity of Church Planting.

• Evangelism is most effective in the context of a local church. People who are “evangelized” in the context of an ongoing worshipping and shepherding community are much more likely to come into vital, saving faith.
  
  
• New churches are by far the best way to reach new generations, new residents, and new people groups.
  
  
• New churches best reach the unchurched, period. The average new church gains most of its new members from the ranks of people who are not attending any worshipping body, while churches more than 10 to 15 years old gain 80 to 90 percent of new members by transfer from other congregations.
  
  
• New churches are the only ministries that become self-supporting and expand the base for all other ministries.
  
  
• New churches are the best single way to revitalize older congregations in the area. New churches help the overall body of Christ by a) showcasing new ministry forms and ideas that would never have been adopted in older churches, b) creating an “it can be done” mindset in older churches, c) providing many new converts in the city that find their way to older churches, and d) supporting many new ministries that have city-wide benefits.
  
  
• The only wide-scale way to bring in lots of new Christians to the body of Christ in a permanent way is to plant new churches. To throw this into relief, imagine Town A, Town B and Town C are the same size and they each have 100 churches of 100 persons each. But in Town A, all the churches are more than 15 years old and that the overall number of active Christian churchgoers in that town will be shrinking, even if four or five of the churches get very “hot” and double in attendance. In Town B, five of the churches are under 15 years old, and they along with several older congregations are winning new people to Christ, but this only offsets the normal declines of the older churches. Thus the overall number of active Christian churchgoers in that town will be staying the same. Finally, in Town C, 30 of the churches are under 15 years old. In this town, the overall number of active Christian churchgoers will be on a path to grow 50 percent in a generation.