Collection of writings left in church cell (9)
I believe the answer is:
corpuscle
'cell' is the definition.
(I know that corpuscle is a type of somatic cell)
'collection of writings left in church' is the wordplay.
'collection of writings' becomes 'corpus' (I've seen this in another clue).
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'church' becomes 'CE' (abbreviation for Church of England).
'l' placed within 'ce' is 'cle'.
'corpus'+'cle'='CORPUSCLE'
(Other definitions for corpuscle that I've seen before include "Minute organism in blood" , "Red or white blood cell" , "Cruel cops with blood cell" .)