Intense fire spread over church (6)
I believe the answer is:
fierce
'intense' is the definition.
('fierce' can be similar in meaning to 'intense')
'fire spread over church' is the wordplay.
'spread' indicates an anagram.
'over' says to put letters next to each other.
'church' becomes 'ce' (abbreviation for Church of England).
'fire' anagrammed gives 'fier'.
'fier'+'ce'='FIERCE'
(Other definitions for fierce that I've seen before include "Cruel or intense" , "Intensely violent, savage" , "Ferocious, savage" , "Powerfully intense" , "Barbarous" .)