You must strive to examine your dreams, for they are a manifestation of the Holy One's guidance personally directed to you. Rabbi Shimon bar Yochai, of blessed memory, teaches (see Chapter Four of "Shaarei Kedusha"), that you can analyze your behavior through a dream, for according to what you do during the day, so is the dream (Zohar, Chaya Sarah 130a). As Elijah said to Job, "In a dream, a nocturnal vision of the night, when a deep sleep falls over people, during slumbers upon the bed, then He uncovers people's ears and seals their affliction." (Job 33:15)
To the extent that a person is righteous, so is the truth of his dreams….
To the extent that a person is righteous, so is the truth of his dreams. A person will sometimes see visions of the heavenly worlds in his dreams, and there will speak with the deceased and recognize them; these will reveal to the dreamer teachings about the Garden of Eden and Gehinom, as it has often happened in our times. Yet, I do not want to lengthen this essay with stories. Our sages say, "Rabbi Yonah said in the name of Rabbi Zera, 'One who does not have a dream for seven consecutive days is a transgressor, as the verse says, 'And he who has it will rest satisfied [in Hebrew, 'savea'] and will not be visited for evil.' (Proverbs 19:23) Do not read 'savea' bur 'sheva' [Hebrew for 'seven']." (Berachot 14a)
Rashi, of blessed memory, explains that a person who transgresses does not receive the guidance of the Divine Providence through a dream. It seems to me that a dream will not come to him because his soul does not ascend on high while he sleeps. The soul of such a person is like the spirit of the beast that descends to the depths of the earth [paraphrasing Ecclesiates 3:21].
What is decreed for man in the heavenly worlds is revealed through dreams. As Rabbi Shimon bar Yochai explains: "Thirty days before a nation rises to power, or before a nation is to endure a disaster, the coming event is announced throughout the world. It is sometimes communicated through the mouths of children, or that of the simple-minded, or at times through birds who proclaim it to the world, but no one is aware of this because no one understands. When the nation is worthy, the impending misfortune is announces to the righteous leaders of the generation so that these may issue a warning; thus, when the people hear about the decree they may return to their Maker. Yet, if the people are not deserving, it is as we said." (Zohar, Shemot 6b)
[Translated by Simcha Benyosef]