Why is sexual magic so important for spiritual development?

When a couple is united sexually, clairvoyants often see a very bright light enveloping the couple.  Precisely in that moment the creative forces of Nature serve as a medium for a new being.  When the couple lets itself go in carnal passion, and later commits the crime of spilling the semen, these luminous forces withdraw, and in their place, satanic forces penetrate, luciferic forces of a bloody red color that bring quarrels, jealousy, adultery, weeping and desperation to the home.  That is how homes that could be a heaven on Earth become true infernos.  People who do not spill their semen, retain and accumulate for themselves peace, abundance, wisdom, happiness and love.  Arguments within homes can be eliminated with the key of sexual magic; this is the key to true happiness.

During the act of sexual magic, couples charge themselves with magnetism; they mutually magnetize each other.  In the woman the pelvis emanates feminine currents, while her breasts give off masculine ones.  In the man the feminine current emanates from the mouth, and the masculine one from his virile member.  All of these organs must be well excited through sexual magic in order to give off and receive, transmit and retrieve vital magnetic forces that increase extraordinarily in quantity and quality.

In the home of Gnostic initiates, the objective of delightful dances, joyful music and ardent kisses, where couples come into intimate sexual contact, is the mutual magnetization of man and woman.  The magnetic power is masculine and feminine at the same time.  The man needs the fluids of his wife if he truly wishes to progress, and the woman inevitably needs the fluids of her husband in order to develop all of her powers.

When a couple mutually magnetizes each other, daily business progresses and happiness makes a nest in the home.  When a man and woman unite, something is created.  Scientific chastity allows the transmutation of the sexual secretions into Light and Fire. - Samael Aun Weor, The Perfect Matrimony

Sexuality is both a creator and a destroyer. The creative forces of sex crystallize a new, superior nature within the practitioner, while the destructive forces remove one's inferior nature related with our evolution through the animal kingdom. This is the basis of being "born again."

This superior nature is collectively called the soul, or more descriptively, the Solar Bodies. These are three vestments of one's Innermost that are formed through the saturation of the transmuted sexual energy upon three successive octaves of energy. They are called the Solar Astral Body, the Solar Mental Body, and the Solar Casual Body and carry out the principles of emotion, thought, and will respectively.

In the current human (or better stated "intellectual animal"), these three principles manifest themselves through three inferior vestments related to a collective, animal nature. In sum they are referred to as the ego. Thus, instead of a Solar Astral Body, one has a Body of Desire or Kama Rupa, instead of a Solar Mental Body one has a Lunar Mental Body, and instead of a Solar Casual Body one has the Animal Will of a legion of psychological aggregates.

Through sexual magic the aspirant can crystallize the Solar Bodies and begin to receive God is a superior fashion, yet, this does not denote the removal of the Lunar Bodies. When the Solar Bodies are being formed and the Lunar Bodies have not been destroyed, then that soul possesses a double center of gravity, one angelic and another that is diabolic. Therefore it is necessary to disintegrate the Lunar Bodies. The Lunar Bodies are destroyed through the means of a revolutionary psychology, which when enacted correctly bring about psychological death (destruction of the ego). In brief this calls for the employment of self-observation and a dedicated routine of meditation to bring forth comprehension concerning one's own defects and vices. While a certain percentage of ego can be eliminated as a single person, the summit of psychological death is found within sexual magic itself. This is done by pleading one's own individual Divine Mother for the destruction a particular ego-aggregate that has previously been comprehended through the science of meditation. Read The Mystery of the Golden Blossom for more information.