Self-denying sailors can finally purchase books (9)
I believe the answer is:
abstinent
'self-denying' is the definition.
(I've seen this before)
'sailors can finally purchase books' is the wordplay.
'sailors' becomes 'abs' (I've seen this in other clues**).
'can' becomes 'tin' ('tin' can be a synonym of 'can').
'finally' indicates one should take the final letters.
'books' becomes 'nt' (New Testament).
The last letter of 'purchase' is 'e'.
'abs'+'tin'+'e'+'nt'='ABSTINENT'
(Other definitions for abstinent that I've seen before include "Restrained" , "without booze" , "Going without, especially food and alcohol" , "Keeping off alcohol" , "self-control" .)