Clergymen soon appearing in empty churches (6)
I believe the answer is:
canons
'clergymen' is the definition.
(canon is a kind of clergyman)
'soon appearing in empty churches' is the wordplay.
'soon' becomes 'anon' (synonyms).
'appearing in' means one lot of letters goes inside another.
'empty' means to remove the middle letters.
'churches' with its centre removed is 'cs'.
'anon' inserted into 'cs' is 'CANONS'.
(Other definitions for canons that I've seen before include "Large guns" , "These members of the clergy sound like big guns" , "Fundamental principles generally accepted in a particular field" , "Officially accepted collections of writings" , "Bodies of rules or principles, in religions say" .)