Song and religious instruction given in AA (4)
I believe the answer is:
aria
'song' is the definition.
(aria is a kind of song)
'religious instruction given in aa' is the wordplay.
'religious instruction' becomes 'RI' (abbreviation).
'given in' is an insertion indicator.
'ri' going within 'aa' is 'ARIA'.
'and' is the link.
(Other definitions for aria that I've seen before include "Operatic vocal" , "Elaborate accompanied song for solo voice" , "Air in an opera" , "Operatic tune" , "Song from an opera (4)" .)