Church contained within state apparatus (7)
I believe the answer is:
machine
'apparatus' is the definition.
(I've seen this in another clue)
'church contained within state' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'contained within' is an insertion indicator.
'state' becomes 'maine' (US state).
'ch' inserted inside 'maine' is 'MACHINE'.
(Other definitions for machine that I've seen before include "Nice ham (anag.)" , "Chain me to power-driven apparatus" , "Device providing energy to perform a task" , "Automaton" , "Industrial worker" .)