Pranava

Pranava (devanāgarī: प्रणव praṇava) is a Sanskrit word that literally means "that which is sounded out loudly", and is used to refer to the mystical sound Om (ओ, "aum"). The pranava, of Hindu origin, is regarded as sacred in Hinduism, Buddhism and Jainism. This syllable is also referred to as omkara (ओंकार) or aumkara (औंकार), literally "om syllable".

In Theosophy

Mme. Blavatsky wrote in The Theosophical Glossary:

Om or Aum (Sk.). A mystic syllable, the most solemn of all words in India. It is “an invocation, a benediction, an affirmation and a promise”; and it is so sacred, as to be indeed the word at low breath of occult, primitive masonry. No one must be near when the syllable is pronounced for a purpose. This word is usually placed at the beginning of sacred Scriptures, and is prefixed to prayers. It is a compound of three letters a, u, m, which, in the popular belief, are typical of the three Vedas, also of three gods-A (Agni) U (Varuna) and M (Maruts) or Fire, Water and Air. In esoteric philosophy these are the three sacred fires, or the “triple fire” in the Universe and Man, besides many other things. Occultly, this “triple fire” represents the highest Tetraktys also, as it is typified by the Agni named Abhimânim and his transformation into his three sons, Pâvana, Pavamâna and Suchi, “who drinks up water”, i.e., destroys material desires. This monosyllable is called Udgîtta, and is sacred with both Brahmins and Buddhists.

In her teachings, the Aum corresponds to the "upper triangle", where Buddhi is the second letter and the Higher Ego the third:

The AUM contains the evocation of the Vedic triad, the Trimurti Brahma, Vishnu, Siva, say the Orientalists; it contains the evocation of something more real and objective than this triune abstraction — we say, respectfully contradicting the eminent scientists. It is the trinity of man himself, on his way to become immortal through the solemn union of his inner triune SELF.

It [the Om] represents the forever-concealed primeval triune differentiation, not from but in the ONE Absolute, and is therefore symbolized by the 4, or the Tetraktys, in the metaphysical world. It is the Unit-ray, or Atman. It is Atman, this highest spirit in man, which, in conjunction with Buddhi and Manas, is called the upper Triad, or Trinity.

Effects of its chanting

Mme. Blavatsky states that from the Esoteric Brahmanical point of view the "Ineffable Name" or AUM is "to be pronounced only mentally, under penalty of death". She adds that it "is a mystic term pronounced by the Yogis during meditation . . . with breath suppressed.

According to her, the chanting of Aum is a "conjuration of, or appeal to, non-human PRESENCES." However, this is not the only effect, because it can reach the person's Higher Self:

The word Aum or Ôm, which corresponds to the upper triangle, if pronounced by a very holy and pure man, will draw out or awaken, not only the less exalted potencies residing in the planetary spaces and elements, but even his Higher Self, or the “Father” within him. Pronounced by an averagely good man, in the correct way, it will strengthen him morally, especially if between two “Aums” he meditates intently on the Aum within him, concentrating all his attention upon the ineffable glory. But woe to the man who pronounces it after the commission of some far-reaching sin: he will thereby only attract to his own impure photosphere invisible presences and forces which could not otherwise break through the divine envelope.

The power of mantras such as the OM is based on the fact that its chanting awakens the forces present in Ākāśa:

Students in the West have little or no idea of the forces that lie latent in Sound, the Âkâsic vibrations that may be set up by those who understand how to pronounce certain words. The Om, or the “Om mani padme hûm” are in spiritual affinity with cosmic forces, but without a knowledge of the natural arrangement, or of the order in which the syllables stand, very little can be achieved. . . Now, letters, as vocal sounds, cannot fail to correspond with musical notes, and therefore with numbers and colors; hence also with Forces and Tattvas. He who remembers that the universe is built up from the Tattvas, will readily understand something of the power that may be exercised by vocal sounds.

According to Mme. Blavatsky the potency of a mantra lies "in the rhythm or the accent". There are different ways to pronounce the Aum:

“Om” is, of course, Aum, that may be pronounced as two, three or seven syllables, setting up different vibrations.

Additional resources

Articles

*Aum! by William Q. Judge
* Aum in Theosophy World