Enthusiastic about books in different bits (4)
I believe the answer is:
into
'enthusiastic about' is the definition.
(I've seen this before)
'books in different bits' is the wordplay.
'books' becomes 'nt' (abbreviation for New Testament).
'in' indicates putting letters inside.
'different bits' becomes 'io' (resembling 1 and 0, both bits in computing. I am not sure about the 'different' bit.).
'nt' inserted within 'io' is 'INTO'.
Can you help me to learn more?
(Other definitions for into that I've seen before include "To a position within" , "Keen on (informal)" , "Curious about" , "A fan of" , "digging" .)