Shocks friend, stuck in part of church briefly (6)
I believe the answer is:
appals
'shocks' is the definition.
('appal' can be a synonym of 'shock')
'friend stuck in part of church briefly' is the wordplay.
'friend' becomes 'pal' (pal is a kind of friend**).
'stuck in' means one lot of letters goes inside another.
'part of church' becomes 'apse' ('apse' is part of 'church').
'briefly' means to remove the last letter.
'apse' with its final letter removed is 'aps'.
'pal' inserted inside 'aps' is 'APPALS'.
(Other definitions for appals that I've seen before include "Fills with disgust" , "'Horrifies, outrages (6)'" , "Fills with dismay or horror (6)" , "Shocks" .)