Who do you think is the most important person in a play? The lead character? Well, for the audience, maybe... But for you, as an actor, it will be the director! This is the person who interprets a play in a certain way. One script, directed by two different directors, will most likely result in two very different plays!
You could think of the director as your boss and teacher combined in one person. He will have an overview of the play, a picture of the whole play in his mind already - Where you may see just a boring rehearsal room with some ugly wallpaper, he sees a big Victorian wall with a great white balcony, surrounded by beautiful purple Wisterias.