Gospel turns on church body (7)
I believe the answer is:
evangel
'gospel' is the definition.
(I know that evangel is a class)
'turns on church body' is the wordplay.
'turns' is a reversal indicator.
'on' becomes 'leg' (cricket term, fielding positions).
'church body' becomes 'nave' (part of a church building).
'leg'+'nave'='legnave'
'legnave' written backwards gives 'EVANGEL'.
(Other definitions for evangel that I've seen before include "Christian gospel" , "Gospel of the New Testament" , "Name applied to any of the four main Gospels" , "good news for Christians!" , "Matthew maybe" .)