Great deal of service (4)
I believe the answer is:
mass
I believe this clue is a double definition.
'great deal' is the first definition.
(synonyms)
'service' is the second definition.
(kind of church service)
'of' is the link.
(Other definitions for mass that I've seen before include "Matter; large amount" , "Service; horde" , "Body of matter" , "Get together" , "Quantity; religious service" .)