Largely failing to save edition of holy books (5)
I believe the answer is:
vedic
'of holy books' is the definition.
(relating to the Veda)
'largely failing to save edition' is the wordplay.
'largely failing' becomes 'vic' (I can't explain this - if you can you should give a lot more credence to this answer).
'to save' means one lot of letters goes inside another.
'edition' becomes 'ed'.
'vic' enclosing 'ed' is 'VEDIC'.
(Other definitions for vedic that I've seen before include "of ancient texts" , "religious language" , "Sort of language" .)