They are prophetic dreams.
Dreams were though of as a "threshold" from the daylight to the darkness, life and death. And the barrier that was in between, was man's fear of death. Throughout history, figures in dreams have been thought of as "souls of the dead," and messengers from the spirit world here to open up your spirit to guidance and divination. If you were able to accept the messages that came to you in your dreams, you were at peace with death and could accept what comes.