Brother's style indeed shown after Mass (7)
I believe the answer is:
tonsure
'brother's style indeed' is the definition.
I can't judge whether this definition defines the answer.
'shown after mass' is the wordplay.
'shown' becomes 'sure' (I can't justify this - if you can you should believe this answer much more).
'after' means one lot of letters go next to another.
'mass' becomes 'ton'.
'sure' after 'ton' is 'TONSURE'.
Can you help me to learn more?
(Other definitions for tonsure that I've seen before include "Monastic hairstyle" , "bare patch" , "Shaven spot on monk's head" , "Haircut for a monk" , "Partial shaving of head" .)