Top cleric's scripture class fills course (7)
I believe the answer is:
prelate
'top cleric's' is the definition.
'prelate' can be an answer for 'cleric's' (I've seen this before). I'm not certain of the 'top' bit.
'scripture class fills course' is the wordplay.
'scripture class' becomes 'RE' (abbreviation for Religious Education).
'fills' means one lot of letters goes inside another.
'course' becomes 'plate' (plate is a kind of course).
're' inserted inside 'plate' is 'PRELATE'.
Can you help me to learn more?
(Other definitions for prelate that I've seen before include "Bishop or other ecclesiastical dignitary" , "Pleater (anag.)" , "Cleric" , "Church high-ranker" , "Senior member of the clergy" .)