Book plays a part (4)
I believe the answer is:
acts
I believe this clue is a double definition.
'book' is the first definition.
(book of the Bible)
'plays a part' is the second definition.
(to act is to play a part)
(Other definitions for acts that I've seen before include "Takes steps" , "religious work" , "Laws passed" , "Decrees" , "Cast in major play sections" .)