When a person sleeps, he is at the level of being that is free from the mind freed from prejudice and control "ego". With this in front of him opened up broader prospects, other horizons of reality. If you say differently, it is most optimal moment to listen to the Divine revelation - is the moment when we are making the least effort to make themselves look.
Sleep is the time at which the divine reality penetrated the consciousness of man, much appreciated by all the major religions - Christianity, Judaism, Taoism, Islam. At the same time, each in its own way knows exactly how God is in contact with humanity. It would be worth mentioning that the dreams in which there was communication with God, the source of both objective and subjective foresight (ie, based on the individual, their own values of a specific person). In other words, you do not worry about how you passed the divine message (through an object or person), - let the message itself keeps you on the right path.