1. “A good person is not shown a good dream”
Since the purpose of a dream is to cause a person to repent, a good person is shown a bad dream to facilitate his repentance. A bad person is shown good dreams as part of his punishment, since his repentance is not desired (HaKotev). Even though there are cases where good dreams were experienced by good people, e.g., the biblical Joseph, that is when seeing the dream plays a role in its realization (Tziyyun LeNefesh Hayya).
2. “Anyone who sleeps seven days without a dream is called evil”
The idea that going without a dream for an extended period happens to the evil can be explained by understanding that dreams are an expression of the subconscious thoughts of a person during the day, as the Gemara derives from the book of Daniel (2:29). It is clear that every person has inappropriate thoughts that they regret. Even people who carry out wicked deeds usually regret their actions and want to repent. Many dreams are an unconscious manifestation of these thoughts. Consequently, one who has no dreams for seven days must have performed some evil deed and did not even consider repenting (Iyyun Ya’akov).
3. One who saw a dream and does not know what he saw should stand before the priests when they lift their hands during the Priestly Blessing and say a prayer that the dream should be interpreted in a positive manner.
One approach to this statement understands that it refers to someone who does not know whether the dream that he saw was good or bad. This approach suggests that, in addition to reciting the formula for bettering a dream, he should also recite this prayer during the Priestly Blessing (Eliya Rabba). The Maharsha suggests that only one who saw a disturbing dream recites the formula for bettering a dream. The prayer recited during the Priestly Blessing is recited only by one who wakes up upset by his dream but has no recollection of its content.