Strength in support of church (5)
I believe the answer is:
force
'strength' is the definition.
(I know that strength can be written as force)
'in support of church' is the wordplay.
'in support of' becomes 'for' (as in being for a particular cause).
'church' becomes 'CE' (Church of England).
'for'+'ce'='FORCE'
(Other definitions for force that I've seen before include "Might" , "Power; army" , "Energy" , "Powerful effect or influence" , "Compel through superior strength" .)