Purists needing education to wear trousers (7)
I believe the answer is:
pedants
'purists' is the definition.
'education to wear trousers' is the wordplay.
'education' becomes 'ed' (abbreviation - e.g. sex ed).
'to wear' becomes 'pants' (pants is a kind of wear**).
'trousers' is an insertion indicator (to trouser can mean to contain or hold).
'ed' inserted within 'pants' is 'PEDANTS'.
'needing' acts as a link.
(Other definitions for pedants that I've seen before include "They are over-concerned with correctness of detail" , "More than one lover of accuracy" , "Paraders of knowledge" .)