Religious work that involves one more duty (11)
I believe the answer is:
deuteronomy
'religious work' is the definition.
The definition suggests a singular noun which matches the answer.
'involves one more duty' is the wordplay.
'involves' indicates an anagram.
'one'+'more'+'duty'='onemoreduty'
'onemoreduty' is an anagram of 'DEUTERONOMY'.
'that' is the link.
Can you help me to learn more?
(Other definitions for deuteronomy that I've seen before include "Old cat in T.S.Eliot's" , "OT book" , "Fifth book of the Bible" , "Book of the Old Testament" .)