Large books finally deter unworthy intolerance (7)
I believe the answer is:
bigotry
'intolerance' is the definition.
(I know that bigotry is a type of intolerance)
'large books finally deter unworthy' is the wordplay.
'large' becomes 'big' (synonyms).
'books' becomes 'OT' (abbreviation for Old Testament).
'finally' says to take the final letters.
The final letters of 'deter unworthy' are 'ry'.
'big'+'ot'+'ry'='BIGOTRY'
(Other definitions for bigotry that I've seen before include "Blind zeal" , "Stubborn prejudice" , "Intolerance, prejudice on grounds of religion" , "Intolerant prejudice" .)