Brewer's agent's truly religious figure (5)
I believe the answer is:
yeast
'brewer's agent's' is the definition.
(chemical agent used when brewing alcohol)
'truly religious figure' is the wordplay.
'truly' becomes 'yea' (I've seen this in another clue).
'religious figure' becomes 'st' (abbreviation for saint).
'yea'+'st'='YEAST'
(Other definitions for yeast that I've seen before include "Brewer" , "Androgynous" , "It's put in to raise" , "Brewer's agent" , "Leavening agent in bread-making" .)