People with servants reduced period in service (7)
I believe the answer is:
masters
'people' is the definition.
(master is a kind of person)
'period in service' is the wordplay.
'period' becomes 'ter' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'service' becomes 'mass' (church service).
'ter' inserted inside 'mass' is 'MASTERS'.
'with servants reduced' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for masters that I've seen before include "Artists of consummate skill" , "Boys" , "Could be checkers" , "Male teachers" , "competition today" .)