Repentant, involving church in witchcraft (7)
I believe the answer is:
sorcery
'witchcraft' is the definition.
(thesaurus)
'repentant involving church' is the wordplay.
'repentant' becomes 'sorry' ('sorry' can be similar in meaning to 'repentant').
'involving' indicates putting letters inside.
'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 "spells etc?" , "Use of magic" , "practice being aligned with the devil?" , "occultism" , "Trickery" .)