Encouragement because the song tell you to be brave and strong
It is dark because Barnardo has trouble seeing the other guard.
Since I haven't read the novel, I would say the general purpose of telling dreams is to share your vision or special event that happened in your imagination. The ability to remember dreams is really good, because most people will forget. While you can tell dreams, try see if you can still visualise the dream. Some dreams can be in black and white, and some can be in colour. Dreams have no limit, they take you to your own little world.
