Faith's tied up, we're told (5)
I believe the answer is:
trust
'faith's' is the definition.
(synonyms)
'tied up we're told' is the wordplay.
'tied up' becomes 'trussed' ('truss' can be a synonym of 'tie up').
'we're told' shows a homophone (sound like).
'trussed' sounds like 'TRUST'.
(Other definitions for trust that I've seen before include "Firm belief (in a thing)" , "Believe" , "Confident expectation" , "'Put your . . . . . In God, and keep your powder dry'" , "Faith (in a business combination?)" .)