Deplorable, involving church in black magic (7)
I believe the answer is:
sorcery
'black magic' is the definition.
(I know this)
'deplorable involving church' is the wordplay.
'deplorable' becomes 'sorry' (synonyms).
'involving' is an insertion indicator.
'church' becomes 'CE' (abbreviation for Church of England).
'sorry' enclosing 'ce' is 'SORCERY'.
'in' is the link.
(Other definitions for sorcery that I've seen before include "Use of magic" , "devilish practices" , "occultism" , "Magic; witchcraft" , "Black magic" .)