Spiritual leader quietly performing rites (6)
I believe the answer is:
priest
'spiritual leader' is the definition.
(priest is a kind of spiritual leader)
'quietly performing rites' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet**).
'performing' indicates anagramming the letters.
'rites' with letters rearranged gives 'riest'.
'p'+'riest'='PRIEST'
(Other definitions for priest that I've seen before include "person of religion" , "Art looking into" , "Religious official" , "Man of god" , "Minister of religion" .)