As papal succession, so topical after Reformation (9)
I believe the answer is:
apostolic
'as papal succession' is the definition.
'apostolic' can be an answer for 'succession' (I have seen 'Such succession' mean 'apostolic' so perhaps 'succession' could also mean 'apostolic'). I'm unsure of the 'as papal' bit.
'so topical after reformation' is the wordplay.
'after reformation' indicates anagramming the letters.
'so'+'topical'='sotopical'
'sotopical' anagrammed gives 'APOSTOLIC'.
Can you help me to learn more?
(Other definitions for apostolic that I've seen before include "Relating to the Pope as the successor to St Peter" , "Such succession" , "of followers" , "Pope's" , "Like Matthew" .)