Sentence:  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 <WSD>is</WSD> not a sufficient condition for joining ; the presence of other members of similar social and economic level is the sufficient condition . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)