Abandon belief, holding religious teaching to be cowardly (8)
I believe the answer is:
recreant
'cowardly' is the definition.
('recreant' can be similar in meaning to 'cowardly')
'abandon belief holding religious teaching' is the wordplay.
'abandon belief' becomes 'recant'.
'holding' means one lot of letters goes inside another.
'religious teaching' becomes 're' (religious education).
'recant' placed around 're' is 'RECREANT'.
'to be' is the link.
(Other definitions for recreant that I've seen before include "yellow" , "Craven, apostate" , "Cowardly; apostate" , "disloyal" .)