You should know that sometimes a person comprehends, due to God’s inspiring him with this knowledge, that his physical animalistic form is keeping him from what would constitute his fulfillment in terms of it’s obeying the angelic side. Therefore he comes to detest the animalistic side and seeks to shatter its force. He won’t find anything that helps him to do this as much as hunger, thirst, forswearing sex, and practicing vigilance over his tongue, heart, and limbs. Persistence in this is a cure for the sickness of his soul. There follows him one who learned this from the truthful news-bearer [the Prophet] with the witness of his heart, then next the one whom the prophets guided out of solicitude for him, while he did not realize it, so that he gets the benefit of this in the next life through the shattering of the [animalistic] form.
Sometimes a person becomes aware that having the physical nature obey the intellect is his perfection, while his physical nature is rebellious, obeying sometimes and not obeying at other times. Thus he needs training, so he takes up some severe practice such as fasting and imposes it on his physical side and perseveres in fidelity to his pledge, more and more, until he obtains the desired object.
Sometimes he commits a sin, so that he perseveres in fasting for many days oppressing himself in response to the sin in order prevent himself from committing more like it.
Sometimes his lower soul craves women, but he is unable to marry and he fears committing fornication, so he defeats his lust through fasting and this is his saying, may the peace and blessing of God be upon him, “Fasting suppresses sexual desire.” ((Mishkat, p.658; Bukhari, Saum 10, Nikah 2, 3; Ibn Majah; Nisai; Darimi; Ibn Hanbal. “Those who cannot marry should fast, since fasting suppresses sexual desires.” Literally, fasting is a castration for him.))
Fasting is a great good deed which strengthens the angelic [side] and weakens the animalistic. There is nothing like it for polishing the face of the spirit and subjugating the physical nature. Therefore, God, may He be exalted, said, “Fasting is for My sake and I reward it.” ((A hadith qudsi, reporting from God. Mishkat, p.417; Bukhari, Saum 2; Muslim; Nisai; Ibn Majah; Muwatta.))
His sins are forgiven to the extent that the animalistic form is diminished and through this is achieved a great similarity to the angels, so that they love him. The attachment of love helps effect the weakening of the animalistic side and this is his saying, may the peace and blessings of God be upon him, “The bad breath of the one who fasts is sweeter to God than the fragrance of musk.” ((Mishkat, p.417; Bukhari, Saum 2; Muslim; Nisai; Ibn Majah; Muwatta.))
If it is made a common convention it avails against the damages of [poor] conventions. If a community persists in fasting their devils will be chained and the gates of the gardens of Paradise are opened to them and the gates of the fires of Hell are locked against them. ((Based on a hadith. See Miskhat, p.417; Muslim; Nisai; Ibn Majah; Muwatta.))
When a person tries to subjugate the lower soul and eliminate its bad qualities, his act will take on a sanctified form in the World of Images. Among the purest of the gnostics is the one who concentrates on this form, for he is furnished with knowledge from the Unseen World and achieves union with the Divine Essence because of transcendence and sanctification. This is the meaning of his saying, may the peace and blessings of God be upon him, “Fasting is done for My sake and I reward it.”
Sometimes a man comes to understand the harm of his being preoccupied with his worldly affairs and his filling his senses with external stimulation. This is helped by devoting himself to worship ((This refers to the practice of i’tikaf or performing a retreat in a mosque.)) in a mosque designed for prayers, so that it is not possible for him to persist in that [preoccupation]. Even if he cannot completely fulfill this retreat, he should not give it up completely. Thus he snatches opportunities from his situation and retreats in a mosque for as long as is decreed for him. Next there is the person who accepts this wholeheartedly from the truthful news-bringer [the Prophet], and [then comes] the ordinary person who is overcome, as was previously mentioned.
Sometimes a person may fast but he is not able to purify his tongue except through retreating to the mosque. Sometimes he may make a request on the Night of Power (Lailat al-Qadr), and seek a connection with the angels, and this contact is not possible except through doing a retreat in the mosque. You will be given the meaning of the Night of Power, and God knows better.
Taken with permission from the English translation of Hujjat Allah al-Balighah (The Conclusive argument from God) by Prof. Marcia K. Hermansen.