Mean to finish one set of books first (6)
I believe the answer is:
intend
'mean to' is the definition.
(thesaurus)
'finish one set of books first' is the wordplay.
'finish' becomes 'end' ('end' can be a synonym of 'finish'**).
'one' becomes 'i' (Roman numeral).
'set of books' becomes 'nt' (New Testament).
'first' is a charade indicator (letters next to each other).
'i'+'nt'='int'
'end' after 'int' is 'INTEND'.
(Other definitions for intend that I've seen before include "Mean; propose" , "Have as one's plan" , "Mean (to do something)" , "Purport" , "Have as purpose or plan" .)