Unhappy people reformed by a sermon (7)
I believe the answer is:
moaners
'unhappy people' is the definition.
The answer and definition can be both people as well as being plural nouns.
Perhaps you can see an association between them that I can't see?
'reformed by a sermon' is the wordplay.
'reformed' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'a' next to 'sermon' is 'asermon'.
'asermon' is an anagram of 'MOANERS'.
Can you help me to learn more?
(Another definition for moaners that I've seen is " People crying".)