Article set for messenger (5)
I believe the answer is:
angel
'for messenger' is the definition.
(heavenly messenger)
'article set' is the wordplay.
'article' becomes 'an' (indefinite article).
'set' becomes 'gel' (both can mean to harden).
'an'+'gel'='ANGEL'
(Other definitions for angel that I've seen before include "Heavenly being - 21 (anag)" , "Sponsor" , "Theatre supporter" , "Obliging person" , "Heavenly body" .)