Meeting the prince changes the narrator’s life in a lot of ways. More than anything, this new friend helps the narrator see the world in a different light. (Who’s the real lamplighter, then?) Part of the way the prince enables the narrator to see the world differently is by pushing his new friend to define terms that most of us think are obvious and have therefore forgotten the meaning of. That way, the prince learns—and the narrator learns too—what it means to be unique, what it means to tame someone, and what it means to make a friend.
If, as the fox says, one sees better with the heart than with the eyes, then it’s likely people also communicate better with their hearts than they do with their mouths.
One of the most important lesson in The Little Prince is that words aren’t very effective at conveying meaning.