Religious person about to criticise analyst (9)
I believe the answer is:
therapist
'analyst' is the definition.
(thesaurus)
'religious person about to criticise' is the wordplay.
'religious person' becomes 'theist' (theist is a kind of religious person).
'about' is an insertion indicator.
'to criticise' becomes 'rap' (I've seen this before).
'theist' enclosing 'rap' is 'THERAPIST'.
(Other definitions for therapist that I've seen before include "One who treats or heals" , "Healer of disease" , "healing type" , "Provider of relieving 57 Across" , "Health worker" .)