Song for church service (3,5)
I believe the answer is:
air force
'service' is the definition.
(air force is a kind of service)
'song for church' is the wordplay.
'song' becomes 'air' (I've seen this before).
'church' becomes 'ce' (abbreviation for Church of England).
'air'+'for'+'ce'='AIR FORCE'
(Other definitions for air force that I've seen before include "Simple tune for church service" , "Junior service" , "Country's military planes" , "Armed service" , "one of the services" .)