Fall back on large recess in church (7)
I believe the answer is:
relapse
'fall back' is the definition.
('relapse' can be a synonym of 'fall back')
'on large recess in church' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'large' becomes 'l'.
'recess in church' becomes 'apse' (I've seen this before).
're'+'l'+'apse'='RELAPSE'
(Other definitions for relapse that I've seen before include "Deteriorate after getting better" , "fall into sin" , "Deteriorate in health" , "Return to sickness" , "setback in health terms" .)