Whole set of books discovered in Ireland (6)
I believe the answer is:
entire
'whole' is the definition.
('entire' can be similar in meaning to 'whole')
'set of books discovered in ireland' is the wordplay.
'set of books' becomes 'nt' (New Testament).
'discovered in' is an insertion indicator.
'ireland' becomes 'eire' ('Eire' can be a synonym of 'ireland').
'nt' going inside 'eire' is 'ENTIRE'.
(Other definitions for entire that I've seen before include "Whole and complete" , "Lure" , "Whole; unbroken" , "With no part left out" , "porter" .)