What Matters More - The Message Or The Messenger?

I learned in the past few weeks that sometimes who is saying something is more important than what is being said. It's caused me to reflect, for some time, on why this is the case? 

When you look at individuals such as President Obama versus former President Bush, when they both say the same thing who would you tend to believe? Over the past 8 years, Bush has proven to be untrustworthy whereas Obama has built a level of credibilty and authority that helps him connect with people in an authentic way. 

In this case the messenger is key. 

However in the case of quotations, we tend to value the message more than the person saying it. How many people believe in "be the change you want to see in the world" because Ghandi said it? It's a quote that resonates with people because there's a connection in the message. You take away from the message what hits true to you, despite who's said it. 

In this case the message is key.

So looking at how we communicate now and taking into consideration the nuances that play a factor into our decision making process, I ask the question: What matters more: "the message or the messenger?"