Person expected to deliver Ashes -- I'm out! (7)
I believe the answer is:
messiah
'person expected to deliver' is the definition.
(someone expected to rescue or 'deliver' people)
'ashes i'm out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'ashes'+'im'='ashesim'
'ashesim' anagrammed gives 'MESSIAH'.
(Other definitions for messiah that I've seen before include "Hallelujah chorus work" , "A hoped-for saviour" , "Handel's composition, sung annually by Our Lady's Choral Society" , "Inspirational liberator" , "Choral work often performed at Christmas" .)