Gather for a service (5)
I believe the answer is:
amass
'gather' is the definition.
(amass can mean to collect or gather)
'a service' is the wordplay.
'service' becomes 'mass' (religious service).
'a'+'mass'='AMASS'
'for' acts as a link.
(Other definitions for amass that I've seen before include "Accumulate over time" , "Collect, hoard" , "Gathers" , "Stockpile" , "Get together" .)