Says, because it's occupied by a retired clergyman (5)
I believe the answer is:
avers
'says' is the definition.
('aver' can be a synonym of 'say')
'because it's occupied by a retired clergyman' is the wordplay.
'because' becomes 'as' (I've seen this in other clues).
'it's occupied by' is an insertion indicator (inserted letters occupy or enter the word).
'a retired' says the letters should be written backwards.
'clergyman' becomes 'rev' (short for reverend).
'rev' in reverse letter order is 'ver'.
'as' enclosing 'ver' is 'AVERS'.
(Other definitions for avers that I've seen before include "Declares to be true" , "States to be true" , "Swears" , "States firmly - really raves" , "States positively" .)