Scrub round entrance to holiest part of church (7)
I believe the answer is:
chancel
'part of church' is the definition.
('chancel' is part of 'church')
'scrub round entrance to holiest' is the wordplay.
'scrub' becomes 'cancel' (I've seen this in another clue).
'round' means one lot of letters goes inside another.
'entrance to' indicates taking the first letters.
The initial letter of 'holiest' is 'h'.
'cancel' enclosing 'h' is 'CHANCEL'.
(Other definitions for chancel that I've seen before include "screened-off area" , "space for choir" , "what's behind the screen" , "where sanctuary may be found" , "Area around the altar of a church" .)