Trader's harangue about church being led by this writer (8)
I believe the answer is:
merchant
'trader's' is the definition.
(thesaurus)
'harangue about church being led by this writer' is the wordplay.
'harangue' becomes 'rant' ('rant' can be a synonym of 'harangue').
'about' means one lot of letters goes inside another.
'church' becomes 'ch' (common abbreviation).
'being led by' says to put letters next to each other.
'this writer' becomes 'me' (the person who is writing these clues).
'rant' enclosing 'ch' is 'rchant'.
'rchant' after 'me' is 'MERCHANT'.
(Other definitions for merchant that I've seen before include "Distributor" , "Wholesale trader" , "One who buys and sells" , "One involved in wholesale trade" , "Antonio, for one" .)