In practice it undermines the transformation of faith. When Christians concentrate their time and energy on their own separate spheres and their own institutions-whether all-absorbing megachurches, Christian yellow-page businesses, or womb-to-tomb Christian cultural ghettoes-they lose the outward thrusting, transforming power that is at the heart of the gospel. Instead of being 'salt' and 'light' -images of a permeating and penetrating action-Christians and Christian institutions become soft and vulnerable to corruption from within.