One brother looks up to grab both boxes (5)
I believe the answer is:
abbot
'one brother' is the definition.
(I've seen this before)
'grab both boxes' is the wordplay.
'boxes' indicates a hidden word (to box can mean to contain).
'ABBOT' can be found hidden inside 'grab both'.
'looks up to' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for abbot that I've seen before include "Superior monk" , "Monks' leader" , "Monastic superior" , "meeting Newton in Devon" , "Head of a community of monks" .)