Fasting:

1. Each person has a duty to subdue his physical aspect. The way to achieve this is through fasting. Fasting weakens the four basic elements of which man is composed and which are the source of all his lusts and impulses. This is the way to humble and nullify the coarse materialism of the body, which is the source of folly and darkness, animality and death. The finer side of man is thereby strengthened and his Divine intellect -- the form as opposed to the substance -- is elevated. The Divine intellect is the soul -- `wisdom,' `light' and `life.' The power of forgetfulness is broken and man remembers his mission in the world. The darkness and harsh judgements are nullified and lovingkindness and blessing are drawn into the world. The main effect of the fast is accomplished through the charity one gives while fasting. (It is customary to give the value of the food one would otherwise have eaten to charity). Through fasting the influence of alien ideologies is thwarted and the wisdom of Torah reigns supreme. Fasting is also a help for one's livelihood (77).
2. In times of danger, God forbid, it is usual to decree a fast. Fasting brings about an illumination of God's favor, and this in itself sweetens and nullifies the harsh judgements, thereby averting the danger. Fasting protects against poverty, degradation and shame and leads to wealth. It also makes us worthy of experiencing miracles (47).
3. When a Tzaddik eats, it is something very precious, because the Tzaddik eats to satisfy his holy soul. Therefore the Tzaddik is forbidden to fast. But one who has to fast should certainly do so. For him it is a mitzvah to fast (50).
4. Fasting is a means of conquering one's anger. In fact this is the main value of a fast. Because of this, the Evil One attacks people with extra force during a fast and tries to make them angry in order to spoil it, God forbid. One must be especially careful to avoid the fire of anger on a fast day. The main value of fasting lies in breaking the force of anger (57:6).
5. Fasting brings a new radiance to the face and restores a person's wisdom -- the very image of God -- and makes it shine on his face. He will be held in awe and respect by those around him and his enemies will fall before him. But in order to spread peace, it is necessary to give charity plentifully (Ibid.).
6. Through fasting it is possible to perfect our speech, and then we can speak before God and pray with devotion. Through perfecting our speech we can draw closer those who were far from God, and this will deepen our faith until it is perfect. It is through faith that we refine the food we eat, and then our eating brings about the unification of the Holy One and the Shechinah face to face (62).
7. Fasting has the power to resolve conflict, both physical and spiritual. When a person is unable to pray or do what he should to serve God, this is `conflict.' Fasting helps to subdue the heart and devote one's will to God alone and make peace (179).
8. Fasting revives the dead. The fast gives life to all the days that were spent in darkness without true vitality. When a person wastes a day by doing no mitzvot or good deeds -- or far worse, by doing actual evil, God forbid -- then that day has no life. It has been `killed.' But all these dead days are brought back to life by fasting. The more a person fasts, the greater the number of dead days he can revive (Ibid.).
9. Fasting brings joy. The more times you fast, the greater the joy (Ibid.).
10. The reason we fast after a bad dream is to draw joy over ourselves by means of the fast. This is the tikkun for the dream. This is why when a person does not want to fast over such a dream, the prayer that is recited says: `Go eat your bread in joy.' Because the main tikkun for the dream is through joy (II, 5:10).
11. On fast days it is a good practice to recite the sections in Leviticus dealing with the sacrifices (Ibid.).