A. There are numerous benefits to fasting, which you can easily find through an online search engine. Physical fasting helps the internal organs to rest, detoxifies the body, and lowers blood pressure. It also helps to reduce blood sugar and increases the breakdown of fats, as well as boosting the immune system.
B. More importantly for us, we need the fast of the spirit. Christ's temptation in the desert represents how the initiate, while working with the transmutation of the sexual energy, must necessarily face the devil (his own mind). Forty days in the wilderness does not necessarily indicate sexual abstention, but how the initiate must comprehend and annihilate the ego by working with the waters (מים Mayim), either in alchemy or through sexual transmutation as a bachelor.
There are periods when the initiate must abstain from sex under command of one's inner יהוה Iod-Chavah. This occurs after reaching Mastery (Tiphereth).
Samael Aun Weor wrote about this in different books, particularly in
The Three Mountains and
The Pistis Sophia Unveiled. After achieving Adepthood, the initiate may be commanded by Christ to take the dry or humid path. The dry path, or sexual abstention after creating the solar bodies, is known as solar brahmacharya. The humid path is continued work in alchemy after achieving Mastery.
"Pseudo-esoteric and pseudo-occult reactionaries suppose they can awaken Kundalini by means of brahmacharya or forced celibacy. All initiates of authentic mystery schools know, through direct experience, that it is impossible to achieve the awakening and development of the seven grades of the power of fire without Tantric practices.
There are two types of brahmacharya (sexual abstention): solar and lunar.
Solar Brahmacharya is obligatory for all those who have already been born in the superior worlds with solar bodies, that is, for those who have left the Ninth Sphere.
Lunar brahmacharya is practiced by many sincerely mistaken people, by many ignoramuses who have never worked in the Ninth Sphere, who have not built the solar bodies, who are without inner self-realization. The practice of lunar brahmacharya is harmful to those who have not built the solar bodies because they become charged with frightfully evil and terrible vibrations.
-Samael Aun Weor, Light from Darkness
The 14th Dalai Lama is an example of a Master who is working in solar brahmacharya. He already has the solar bodies, but is continuing his spiritual work without a partner. Eventually, Christ will command him to descend into the Ninth Sphere again; whether it is in this life or not, who knows?