Wash poor saint found in church (7)
I believe the answer is:
cleanse
'wash' is the definition.
(thesaurus)
'poor saint found in church' is the wordplay.
'poor' becomes 'lean' (**).
'saint' becomes 's'.
'found in' is an insertion indicator.
'church' becomes 'ce' (abbreviation for Church of England).
'lean'+'s'='leans'
'leans' put inside 'ce' is 'CLEANSE'.
(Other definitions for cleanse that I've seen before include "subject to purification" , "give absolution" , "Free of sin" , "Make thoroughly clean" , "clear of muck" .)