A leader needs to communicate in a way that makes people feel what they need to do.
As a leader of a large group you have to keep in mind that people need to believe in you and know that you're behind any given message. It's not only what you say but truly what you feel and believe. This rule reminds all of us, and leaders in particular, that emotions are a powerful motivator -- or, in some cases, a de-motivator. We're social creatures who need interaction, and you use that to make points when they're important enough.
When you deliver a message face-to-face, it's strikingly different than when you do some kind of mass communication. If we're going to have impact as leaders, we have a responsibility to communicate directly, eyeball-to-eyeball, and with authenticity.