A leader holds the vision and then gets the team there, and neither half works if the vision stays inside your head. Saying it out loud sharpens it, because people will tell you when it is unrealistic. It also tells your team what you expect of them. One of my goals is that every camper eventually becomes a counselor, so I say that to campers constantly, even the five-year-olds.
This is the short version. The full lesson, with the story behind it, is in the book.
Take The Summer Camp MBA with you, or get the field notes by email while you work through the lessons here.