Bare minimum of instructional books — effectively treat as one (2,3,10)
I believe the answer is:
in the altogether
'bare' is the definition.
(thesaurus)
'minimum of instructional books effectively treat as one' is the wordplay.
'minimum of' indicates taking the first letters.
'books' becomes 'nt' (New Testament).
'effectively treat' becomes 'heal'.
'as one' becomes 'together' (I've seen this before).
The initial letter of 'instructional' is 'i'.
'i'+'nt'+'heal'+'together'='IN THE ALTOGETHER'
(Other definitions for in the altogether that I've seen before include "wearing nothing?" , "Naked" , "exposed" , "having nothing to wear?" , "barely seen" .)