The key to Protestant development, therefore, is economic integration of the nucleus of the congregation. Members of higher and lower social status often cluster around this nucleus, so that Protestant figures on social class give the impression of spread over all social classes; but this is deceptive, for the core of membership is concentrated in a single social and economic stratum. The congregation perishes when it is no longer possible to replenish that core from the neighborhood; moreover, residential mobility is so high in metropolitan areas that churches have to recruit constantly in their core stratum in order to survive; they can lose higher -- and lower status members from the church without collapsing, but they need adequate recruits for the core stratum in order to preserve economic integration. The congregation is first and foremost an economic peer group; it is secondarily a believing and worshiping fellowship. If it were primarily a believing fellowship, it would recruit believers from all social and economic ranks, something which most congregations of the New Protestantism (with a few notable exceptions) have not been able to do. They survive only when they can recruit social and economic peers.

The vulnerability of Protestant congregations to social differences has often been attributed to the ``folksy spirit'' of Protestant religious life; in fact, a contrast is often drawn in this regard with the ``impersonal'' Roman Catholic parish. We have seen that the folksy spirit is confined to economic peers; consequently, the vulnerability to social difference should not be attributed to the stress on personal community in Protestant congregations; actually, there is little evidence of such personal community in Protestant congregations, as we shall see in another connection. The vulnerability of Protestantism to social differences stems from the peculiar role of the new religious style in middle-class life, where the congregation is a vehicle of social and economic group identity and must conform, therefore, to the principle of economic integration. This fact is evident in the recruitment of new members.