Song and religious instruction in AA (4)
I believe the answer is:
aria
'song' is the definition.
(aria is a kind of song)
'religious instruction in aa' is the wordplay.
'religious instruction' becomes 'RI' (abbreviation).
'in' indicates putting letters inside.
'ri' put within 'aa' is 'ARIA'.
'and' is the link.
(Other definitions for aria that I've seen before include "Operatic number" , "Song for solo voice from an oratorio, cantata etc" , "selection of opera" , "Opera solo" , "Imitative art work" .)