Sentence:  The expense of this type of organization in religious life , when one recalls the number of city churches which deteriorated beyond repair before being abandoned , raises fundamental questions about the principle of Protestant survival in a mobile society ; nonetheless , the prevalence of economic integration in congregations illumines the <WSD>nature</WSD> of the Protestant development . 
Meaning of the word marked with <WSD> tags:  the essential qualities or characteristics by which something is recognized