There are stages in your sleep where you can have dreams. You go through these stages thousands of times of night. Thats why you can sometimes remember multiple dreams a night. Dreams are from your brain. Your mind never shuts off. Your soul has to do with the spiritual realm that most have their different opinions on.
I do believe that the soul can "speak" to us through dreams...not all dreams, but with practice you can learn to discern where a dream originates. Dreams from your soul often come through the primordial language of archetypes...symbols or images that are cross-cultural and universally understood.
This concept of archetypes was developed in modern times by Carl Jung, and explored by Joseph Campbell in books like THE HERO WITH A THOUSAND FACES.