Quietly illuminated following end of religious schism (5)
I believe the answer is:
split
'schism' is the definition.
('split' can be a synonym of 'schism')
'quietly illuminated following end of religious' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'illuminated' becomes 'lit' ('lit' can be a synonym of 'illuminated').
'following' means one lot of letters go next to another.
'end of' says to take the final letters.
The final letter of 'religious' is 's'.
'p'+'lit'='plit'
'plit' after 's' is 'SPLIT'.
(Other definitions for split that I've seen before include "resort on the Adriatic" , "Riven; schism" , "Cause fission of (atom)" , "Dalmatian port" , "Go separate ways" .)