“Nachiketas asked: ‘What lies beyond right and wrong, beyond cause and effect, beyond past and future?’ Death said: ‘The word the Vedas extol, austerities proclaim, sanctities approach – that word is Om. That word is eternal Spirit, eternal distance; who knows it attains to his desire. That word is the ultimate foundation. Who finds it is adored among the saints. The Self knows all, is not born, does not die, is not the effect of any cause; is eternal, self-existent, imperishable, ancient. How can the killing of the body kill him?'”
Katha-Upanishad
Om is the supreme mantra (mystical sound) of Hindu origin, but sacred and important to various religions of Dharmic origin (Hinduism, Buddhism, Jainism…). It is the sound vibration of the Absolute, which lies beneath everything manifested (physical plane, causal plane, subtle plane). It is the sound of silence, the sound of the Self, the sound of Being. The sound “A” represents Creation, like Brahma. The sound “U” represents Conservation, like Vishnu. The sound “M” represents Dissolution, like Shiva. Om is the all encompassing vibration of the Universe.
“The word Om is the Imperishable; all this its manifestation. Past, present, future – everything is Om. Whatever trascends the three divisions of time, that too is Om. There is nothing that is not Spirit. The personal self is the impersonal Spirit. It has four conditions. This Self, though beyond words, is that supreme word Om; though indivisible, it can be divided in three letters corresponding to the three conditions of the Self, the letter “A”, the letter “U”, and the letter “M”. The waking condition, called the material condition, corresponds to the letter “A”, which leads the alphabet and breathes in all the other letters. He who understands,gets all he wants; becomes a leader among men. The dreaming condition, called the mental condition, corresponds to the second letter “U”. It upholds; stands between waking and sleeping. He who understands, upholds the tradition of spiritual knowledge and looks upon everything with an impartial eye. No one ignorant of Spirit is born into his family. Undreaming sleep, called the intellectual condition, corresponds to the letter “M”. It weighs and unites. He who understands, weighs the world; rejects; unites himself with the cause. The fourth condition of the Self corresponds to Om as One, indivisible Word. He is whole; beyond bargain. The world disappears in Him. He is the good; the one without asecond. Thus Om is nothing but Self. He who understands, with the help of his personal self, merges himself into the impersonal Self; He who understands.”
Mandookya-Upanishad
Om. Om. Om.
Journey To The Self 