Asian heretic inspiring a book (7)
I believe the answer is:
arabian
'asian' is the definition.
(Arabia is part of Asia)
'heretic inspiring a book' is the wordplay.
'heretic' becomes 'arian' (Arianism is a form of heresy).
'inspiring' is an insertion indicator.
'book' becomes 'b' (abbreviation for book).
'a'+'b'='ab'
'arian' enclosing 'ab' is 'ARABIAN'.
(Other definitions for arabian that I've seen before include "Asian" , "Type of horse" , "from Bahrain, perhaps" , "Prized horse" , "Of a Middle East area" .)