Stumbles across church army feature! (7)
I believe the answer is:
triceps
'army feature' is the definition.
(an 'army' feature - arm muscles)
'stumbles across church' is the wordplay.
'stumbles' becomes 'trips' ('trip' can be a synonym of 'stumble').
'across' is an insertion indicator.
'church' becomes 'CE' (abbreviation for Church of England).
'trips' enclosing 'ce' is 'TRICEPS'.
(Other definitions for triceps that I've seen before include "One stretches out an arm!" , "Green citrus fruit" , "Muscle that extends the forearm" , "Source of uplifting strength" , "army feature?" .)