I think this is a very important statement. I've struggled over the years with that concept. It is difficult to believe the message if the messenger is without honor. It would make one doubt as to the legitimacy of the message - it could have been corrupted in the pass through.
I watched a movie where a young reporter was given an opportunity to interview a famous Bhuddist. She entered his hotel room and sat down and prepared for the interview. He came over and sat down across from her and flipped open his buddhist robes. You could tell by her face it was obvious he was exposing himself. When she hastily got up to leave exclaiming that she was there for an interview, he told her that "The messenger is not the message." The woman in the movie declined to interview him and left after having her illusions shattered about this man.
This movie scene has stayed with me long after the name has faded. I have come to see that the messenger and the message are very much tied together and that it is the actions of the messenger that tells you whether the message can be trusted or not.
It is the foundation from which I analyze most everything I read. Most things sit on the back burner in my mind until something comes along to either validate the message or negate it. Even then my inner skeptic keeps me from taking the bait.