Jesus is the authority and the Word. The demon in the man represents the devil taunting God; and shows that he can inhabit our thoughts if we don’t turn our thoughts to God.
Jesus proves his authority casting out the devil immediately from the man, curing both his body and soul in an instant. The Good News of this man’s cure is spread far and wide as a result. We need to do the same thing, spreading the message of Jesus and his authority through words and actions.