OT book references the reverend includes (6)
I believe the answer is:
esther
'ot book' is the definition.
(book of the Old Testament)
'references the reverend includes' is the wordplay.
'includes' says the answer is hidden in the clue.
'ESTHER' is hidden in the letters of 'references the reverend'.
(Other definitions for esther that I've seen before include "Biblical heroine, who married the king of Persia" , "Now there's a lady" , "__ Rantzen, TV presenter, b. 1940" , "OT Queen of Persia" , "OT heroine" .)