तस्य वाचक् प्रिव्
tasya vācakaḥ praṇavaḥ
His word is Pranava
tasya = His
vācakaḥ= word, term
Pranava= Om, AUM
His word is Pranava. Pranava is OM. The letter "o" is the combination of short vowels "a" ( as u in the word 'but') and "u" (as u in the word 'put'). The shorter version of Pranava is OM whereas the longer one is AUM.
God is OM. OM invokes God. It invokes the deities. It invokes the demigods. That is why all the mantras of God, the deities or demigods start with Pranava. There is no mantra without Pranava. That means, it is not possible to invoke any deity or demigod without first invoking God.
Commentary by Maharishi Vyasha
The word expressing Him is Pranava
The object expressed by the Pranava is Isvara. Does this expression temporary or Permanent? The relationship between the indicator (Pranava) and the indicated (God) is fixed. It is based on the usage of this indication by Isvara which is similar to the fixation of the relationship between a father and son by the usages like "He is his father" and "He is the son". The fixing of the relationship between the indicator and the indicated is made by Isvara with reference to the earlier creations also. Authoritative sages declare this relationship of the indicator and the Indicated as eternal, because of the commonality of its universal acceptance.
Commentary by Swami Vivekananda
His manifesting word is Om
Every idea that you have in the mind has a counterpart in a word; the word and the thought are inseparable. The external part of the thought is what we call word, and the internal part is, what we call, thought. No man can, by analysis, separate thought from word. The idea that language was created by men—certain men sitting together and deciding on words, has been proved to be wrong. So long as things have existed there have been words and language. What is the connection between an idea and a word? Although we see that there must always be a word with a thought, it is not necessary that the same thought requires the same word. The thought may be the same in twenty different countries, yet the language is different. We must have a word to express each thought, but these words need not necessarily have the same sound. Sounds will vary in different nations.
Our commentator says “Although the relation between thought and word is perfectly natural, yet it does not mean a rigid connection between one sound and one idea.” These sounds vary, yet the relation between the sounds and the thoughts is a natural one. The connection between thoughts and sounds is good only if there be a real connection between the thing signified and the symbol, and until then that symbol will never come into general use. Symbol is the manifest or of the thing signified, and if the thing signified has already existence, and if, by experience, we know that the symbol has expressed that thing many times, then we are sure that there is the real relation between them. Even if the things are not present, there will be thousands who will know them by their symbols. There must be a natural connection between the symbol and the thing signified; then, when that symbol is pronounced, it recalled the thing signified.
The commentator says the manifesting word of God is Om. Why does he emphasise this? There are hundreds of words for God. One thought is connected with a thousand words; the idea, God, is connected with hundreds of words, and each one stands as a symbol for God. Very good. But there must be a generalisation among all these words, some substratum, some common ground of all these symbols, and that symbol which is the common symbol will be the best, and will really be the symbol of all. In making a sound we use the larynx, and the palate as a sounding board. Is there any material sound of which all other sounds must be manifestations, one which is the most natural sound? Om (Aum) is such a sound, the basis of all sounds. The first letter, A, is the root sound, the key, pronounced without touching any part of the tongue or palate; M represents the last sound in the series, being produced by the closed lip, and the U rolls from the very root to the end of the sounding board of the mouth. Thus, Om represents the whole phenomena of sound producing. As such, it must be the natural symbol, the matrix of all the variant sounds. It denotes the whole range and possibility of all the words that can be made. Apart from these speculations we see that around this word Om are centred all the different religious ideas in India; all the various religious ideas of the Vedas have gathered themselves round this word Om. What has that to do with America and England, or any other country? Simply that the word has been retained at every stage of religious growth in India, and it has been manipulated to mean all the various ideas about God. Monists, Dualists, Mono-Dualists, Separatists, and even Atheists, took up this Om. Om has become the one symbol for the religious aspiration of the vast majority of human beings. Take, for instance, the English word God. It conveys only a limited function, and if you go beyond it, you have to add adjectives, to make it Personal, or Impersonal, or Absolute God. So with the words for God in every other language; their signification is very small. This word Om, however, has around it all the various significances. As such it should be accepted by everyone.
Commentary by Sri Osho
HE IS KNOWN AS AUM
And this God, the perfect flowering, is known as aum. Aum is the symbol of the universal sound. In you, you hear thoughts, words, but never the sound of your being. When there is no desire, no need, when the body has dropped, when the mind disappears, what will happen? Then the real sound of the universe itself is heard. That is aum.
And all over the world people have realized this aum. Mohammedans, Christians, Jews, they call it amen. It is aum Zoroastrians, Parsis, call it ahura mazada. That a and m – ahura is from a and mazada is from m – it is aum. They have made it a deity.
That sound is universal. When you stop, you hear it. Right now you are talking so much, chattering within yourself, you cannot hear it. It is a silent sound. It is so silent that unless you have completely stopped you will not be able to hear it. Hindus have called their gods a symbolic name – aum.
Patanjali says, He is known as Aum. And if you want to find a Master, a Master of Masters, you will have to get more and more attuned to the sound of aum, oriented that he will not even leave a single word, and he will not use a single word more.