What's the difference between being preachy and passionate?

I understand that there can be a thin line between preaching and speaking passionately. Barack Obama is a brilliant example of someone who has mastered the art of speaking passionately without becoming preachy. A friend of mine was just telling me about a meeting he was recently asked to join because of his expertise on humanitarian relief work. Mind you, this topic was the topic of discussion. He is marvelously articulate and speaks with such authority and passion that it is fully understandable how people will walk to the ends of the Earth for him. 

After he finished his two minute discussion on the role of humanitarian relief work in several hot-button areas of the world right now, there was dead silence from his boss. I should interject here that he is far more educated and personally vested in this cause than she is, despite the fact that she has seniority. He makes her look good without fail, on every project, and she has often publicly taken credit for work he has done. 

At this meeting, rather than thanking him for his point of view, she responded by addressing the group with, "well, not that that information has anything to do with the issue at hand..." Actually, it had everything to do with the issue at hand. His boss was irritated that he had a more articulate, and opposing view, than the surface comments she was making. What's more my friend is far more genuine than his boss, she knows this, and is unable to level the playing field with him. She closed the conversation saying, "well, I think we've had enough preaching for one day." So ludicrous, it's laughable...

And that started me thinking about the difference between preaching, which often has a negative connotation, and articulately addressing an issue with passion. It comes down to whether the person speaking is talking to hear himself talk and or if he is educating and sharing his point-of-view with his audience. Preaching has a lot of shallow dazzle and speaking with passion has dazzle plus substance. With all of my friend's energy and enthusiasm, my advice to him was to move on to someplace that appreciates and rewards him for everything he has to offer.