(HT: Justin Taylor, who emailed me in order to shame me since he found it first)
A few blurbs...
Once in cities, Christians should be a dynamic counterculture. It is not enough for Christians to simply live as individuals in the city. They must live as a particular kind of community. Jesus told his disciples that they were "a city on a hill" that showed God's glory to the world (Matt. 5:14-16). Christians are called to be an alternate city within every earthly city, an alternate human culture within every human culture, to show how sex, money, and power can be used in nondestructive ways.
This is the only kind of cultural engagement that will not corrupt us and conform us to the world's pattern of life. If Christians go to urban centers simply to acquire power, they will never achieve cultural influence and change that is deep, lasting, and embraced by the broader society. We must live in the city to serve all the peoples in it, not just our own tribe. We must lose our power to find our (true) power. Christianity will not be attractive enough to win influence except through sacrificial service to all people, regardless of their beliefs.
So we must neither just denounce the culture nor adopt it. We must sacrificially serve the common good, expecting to be constantly misunderstood and sometimes attacked. We must walk in the steps of the one who laid down his life for his opponents.