Stop church when finally contrite (5)
I believe the answer is:
cease
'stop' is the definition.
(I know that stop can be written as cease)
'church when finally contrite' is the wordplay.
'church' becomes 'ce' (abbreviation for Church of England).
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'finally' says to take the final letters.
The final letter of 'contrite' is 'e'.
'ce'+'as'+'e'='CEASE'
(Other definitions for cease that I've seen before include "Stop, terminate" , "Political group" , "Stop, give over" , "Culminate" , "Finish, end" .)