One exerting a lot of pull in the church (4-6)
I believe the answer is:
'one exerting a lot of pull' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'in the church' is the wordplay.
I cannot really see how this works, but
'in' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for bell-ringer that I've seen is " Campanologist".)