Dog eats Bible, but it's hard work (7)
I believe the answer is:
travail
'it's hard work' is the definition.
(travail can mean hard work or effort)
'dog eats bible' is the wordplay.
'dog' becomes 'trail' (both can mean to follow).
'eats' is an insertion indicator.
'bible' becomes 'av' (Authorised Version of the Bible).
'trail' placed around 'av' is 'TRAVAIL'.
'but' acts as a link.
(Other definitions for travail that I've seen before include "Use of physical or mental energy; excessive labour..." , "painful exercise" , "Painful or laborious effort, like childbirth" , "Exertion, elbow grease" , "Painful labour" .)