In general, religious interest seems to exist in all parts of the metropolis; congregational membership, however, is another thing. A congregation survives only if it can sustain a socially homogeneous membership; that is, when it can preserve economic integration. Religious faith can be considered a necessary condition of membership in a congregation, since the decision to join a worshiping group requires some motive force, but faith is not a sufficient condition for joining; the presence of other members of similar social and economic level is the sufficient condition.

The breakdown of social homogeneity in inner city areas and the spread of inner city blight account for the decline of central city churches. Central cities reveal two adverse features for the major denominations: (1) central cities tend to be areas of residence for lower social classes; (2) central cities tend to be more heterogeneous in social composition. The central city areas, in other words, exhibit the two characteristics which violate the life principle of congregations of the major denominations: they have too few middle-class people; they mix middle-class people with lower-class residents. Central city areas have become progressively poorer locales for the major denominations since the exodus of middle-class people from most central cities. With few exceptions, the major denominations are rapidly losing their hold on the central city.