Sentence:  The inner life of congregations will prosper so long as like-minded people of similar social and economic level can fraternize together ; the outer life of congregations - the <WSD>suitability</WSD> of the environment to their survival - will be propitious so long as the people in the area are of the same social and economic level as the membership . 
Meaning of the word marked with <WSD> tags:  the quality of having the properties that are right for a specific purpose