27. तस्य वाचक् प्रिव् ॥ २७॥
tasya vachakah prannavah
His manifesting word is Om...
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...
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. 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. 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.

29. तत् प्रत्यक्चेतनाणधगभोऽप्यन्तयामाबावि ॥ २९॥
tatah pratyakchetanadhigamopyantarayabhavashch
From that is gain (the knowledge of) introspection, and the destruction of obstacles.
The first manifestation of this repetition and thinking of Om will be that the introspective power will be manifested more and more, and all the mental and physical obstacles will begin to vanish. What are the obstacles to the Yogi?

28. Through the sounding of the Word and through reflection upon its meaning, the Way is found.
This is a very general paraphrase but conveys nevertheless the correct significance of the terms used in the Sanskrit. Only Vivekananda, among the many translators, gives this interpretation, putting it as follows: "The repetition of the OM and meditating upon its meaning (is the Way)."

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) V (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...

The utterance of OM involves three sounds, those of long au, short u, and the "stoppage" or labial consonant m. To this tripartiteness is attached deep mystical symbolic meaning. It denotes, as distinct yet in union, Brahma, Vishnu, and S'iva, or Creation, Preservation, and Destruction. As a whole, it implies "the Universe." In its application to man, au refers to the spark of Divine Spirit that is in humanity; u, to the body through which the Spirit manifests itself; and m, to the death of the body, or its resolvement to its material elements. With regard to the cycles affecting any planetary system, it implies the Spirit, represented by au as the basis of the manifested worlds; the body or manifested matter, represented by u, through which the spirit works; and represented by m, "the stoppage or return of sound to its source," the Pralaya or Dissolution of the worlds. In practical occultism, through this word reference is made to Sound, or Vibration, in all its properties and effects, this being one of the greatest powers of nature. In the use of this word as a practice, by means of the lungs and throat, a distinct effect is produced upon the human body. In Aphorism 28 the name is used in its highest sense, which will necessarily include all the lower. All utterance of the word OM, as a practice, has a potential reference to the conscious separation of the soul from the body.

Om is the mysterious cosmic energy that is the substratum of all the things and all the beings of the entire universe. It is an eternal song of the Divine. It is continuously resounding in silence on the background of everything that exists.

The mantra Om Mani Pädme Hum is easy to say yet quite powerful, because it contains the essence of the entire teaching. When you say the first syllable Om it is blessed to help you achieve perfection in the practice of generosity, Ma helps perfect the practice of pure ethics, and Ni helps achieve perfection in the practice of tolerance and patience. Pä, the fourth syllable, helps to achieve perfection of perseverance, Me helps achieve perfection in the practice of concentration, and the final sixth syllable Hum helps achieve perfection in the practice of wisdom.

Om is not just a sound or vibration. It is not just a symbol. It is the entire cosmos, whatever we can see, touch, hear and feel. Moreover, it is all that is within our perception and all that is beyond our perception. It is the core of our very existence.

When Siddhartha listened attentively to this river, to the song of a thousand voices; when he did not listen to the sorrow or laughter, when he did not bind his soul to any one particular voice and absorb it in his Self, but heard them all, the whole, the unity; then the great song of a thousand voices consisted of one word: Om — perfection.