A few words posted in French church (8)
I believe the answer is:
sentence
'a few words' is the definition.
(I've seen this before)
'posted in french church' is the wordplay.
'posted' becomes 'sent' ('send' can be a synonym of 'post').
'in french' becomes 'en' ('en' can be French for 'in' e.g. en France).
'church' becomes 'ce' (abbreviation for Church of England).
'sent'+'en'+'ce'='SENTENCE'
(Other definitions for sentence that I've seen before include "Punishment awarded by court, or a set of words" , "It makes sense" , "delivered in a few words" , "Grammatical unit and prison term" , "Unit of writing" .)