Choose page in Old Testament (3)
I believe the answer is:
opt
'choose' is the definition.
(both can mean to pick something)
'page in old testament' is the wordplay.
'page' becomes 'p'.
'in' indicates putting letters inside.
'old testament' becomes 'ot'.
'p' put within 'ot' is 'OPT'.
(Other definitions for opt that I've seen before include "Plump for" , "Elect" , "Make a choice" , "Hold in the highest esteem" , "Prefer, choose" .)