High-ranking clergymen, say, needed to fill empty pews (8)
I believe the answer is:
prelates
'high-ranking clergymen' is the definition.
(I've seen this before)
'say needed to fill empty pews' is the wordplay.
'say' becomes 'relate' (as in relating a story).
'needed to fill' means one lot of letters goes inside another.
'empty' means to remove the middle letters.
'pews' with its centre removed is 'ps'.
'relate' put within 'ps' is 'PRELATES'.
(Other definitions for prelates that I've seen before include "Bishops" , "High-ranking clergymen" , "Senior church dignitories" , "Church dignitaries" , "Senior clergy" .)