Opposes religious teaching on part of the bible (6)
I believe the answer is:
reacts
'opposes' is the definition.
('react' can be a synonym of 'oppose')
'religious teaching on part of the bible' is the wordplay.
'religious teaching' becomes 're' (religious education).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'part of the bible' becomes 'Acts' ('Acts' is part of 'bible').
're'+'acts'='REACTS'
(Other definitions for reacts that I've seen before include "Responds to stimulus (6)" , "Retaliates" , "Acts in response to something" , "Responds to an impulse" .)