In favour of them providing a preface (5)
I believe the answer is:
proem
'a preface' is the definition.
(thesaurus)
'in favour of them' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'them' becomes 'em'.
'pro'+'em'='PROEM'
'providing' acts as a link.
(Other definitions for proem that I've seen before include "introduction" , "Prelude" , "Preliminary part" , "introductory piece" .)