Like a fateful day, providing incidental messages (6)
I believe the answer is:
asides
'incidental messages' is the definition.
(something said as an aside might be incidental)
'like a fateful day' is the wordplay.
'like' becomes 'as'.
'a fateful day' becomes 'ides' (ides of March, date of Caesar's assassination).
'as'+'ides'='ASIDES'
'providing' is the link.
(Other definitions for asides that I've seen before include "Actors' remarks in an undertone" , "not everyone hears them" , "Undertones on stage" , "Daises (anag.)" , "Words spoken so that certain people won't hear" .)