The syllable Om is first mentioned in the Upanishads, a part of the Vedas, ancient Sanskrit texts that contain some of the central philosophical concepts and ideas of Hinduism.
The concepts of Brahman (ultimate reality) and Ātman (soul, self) are central ideas of the Upanishads, and "know that you are the Ātman" is their thematic focus.
The Upanishads are commonly referred to as Vedānta. Vedanta has been interpreted as the "last chapters, parts of the Veda" and alternatively as "object, the highest purpose of the Veda".
The syllable Om has variously been associated with concepts of "cosmic sound" or "mystical syllable" or "affirmation to something divine", or as symbolism for abstract spiritual concepts in the Upanishads.
In the Aranyaka and the Brahmana layers of Vedic texts, the syllable is so widespread and linked to knowledge, that it stands for the "whole of Veda" (all there is to know).
The Brahmana layer of Vedic texts offers various shades of meaning to Om, such as it being that which is "mysterious and inexhaustible", or "the infinite language, the infinite knowledge", or "essence of breath, life, everything that exists", or that "with which one is liberated".
Vedic scholars state that Upanishads recommend Om syllable as a "tool for meditation". They say that the Om syllable may appear in the mind of the meditator as "highest concepts such as the cause of the Universe, essence of life, Brahman, Atman, and Self-knowledge".
Now this is very interesting.
In my article "Vowels" I talk about natural meaning associated with pure vowels "A, O, U, E, I" in Serbian language.
Here is the relevant bit:
I will finish with OM - the sacred sound of Vedas.
In Serbian "Budi" means "Be, Exist". "Budan" means awake. Buda was the awaken one, he was Budan (awake).
Buda claimed that "being awake" was "all knowledge"...
The holy sound of Vedas which is said to represent "the whole of Vedas", is OM, pronounced as "AUM"
I actually believe that this sound was originally AOUM but that O was lost first only for AU to be later replaced with O.
AOUM consists of these vowels:
A - outside
O - surface of the body
U - inside of the body
M - core.
M is the only sound that can be made with your mouth closed. It is created by the vibration of the whole central cavity, our core. This is why M is the core sound of words that mean me, my, myself (me, mene in Serbian), the words whose meaning is directed inwards.
So the above mantra brings our focus from outside into our core, (m)ind by using emotional discharge through descending vowels.
The word for mind in Serbian is UM. This word derives its meaning from U + M = inside + me = mind. This is probably the old "AOUM" shortened down to the absolute minimum number of sounds necessary to convey the intended meaning of internal me, real me....mind, UM.
This is kind of incredible, right?
AOUM, through its inner natural meaning encoded in its sound, conveys all the above Vedic teachings.
It is "All of Vedas".
It is "The meditation tool".
It leads us to "Brahman (The Creator, God, The ultimate reality), Atman (Soul which is part of the Ultimate Reality), and Self-knowledge (Realisation that I am Brahman, God)...
Interestingly the root "UM" meaning mind is found in Sumerian language as the root for words related to knowledge, intelligence, ability, respect...
To use the words from one of my favourite songs by Amy Winehouse, "Me and Mr. Jones": "What kind of fuckery is this?"