Here are some highlights from the article. You can read the article here.
There are 3 layers for influence:
1. A contextualized biblical gospel theology- a ‘God ordained third way between legalistic moralism and licentious relativism.” We need to prevent both extremes. Martin Luther famously said that the church errors in these ways like, “A drunk man, having fallen off the horse on one side, gets back up and falls off on the other.”
A church needs to also have a Contextualized Gospel- Keller notes that contextualization has more to do with culture than theology. We can have maturity in theology but not engage the city in a useful way. This may be the tale of many churches in cities today. Keller also gives the warning of over-adapting. Al Hsu also notes that a local church should try to be contextual and counter-cultural in tension.
2. Church Multiplying Movements from a wide variety of traditions. The general ethos of a city, then, would be a missional one in tone. Different faith tribes have much to offer. Keller implores Christians to be Christian first, and their faith tribe second. If many tribes in a city have vibrant and growing churches, planting churches routinely, etc., then the whole city begins to have vibrant churches in more places.
3. Ecosystem of ministry networks- Keller recommends ways for churches to influence and nurture one another. He gives 7 different kinds of networks:
a. City-wide prayer
b. Specialist evangelism, movements reaching people of various ages, locations, stages, nationalities, regions.
c. Justice and Mercy
d. Vocational faith/work initiatives
e. Institutions that support the family in the city
f. Institutions of theological training
g. Christian leaders coming together
Keller feels that a critical mass and tipping point happens when 10-20% of the population (civic and social culture is recognized as reached).
Keller feels that new church starts are important, citing that new churches reach Non-Christians at a rate of 5-7 times the rate of older churches.