In the Bhagavad-gītā (8.13) the glories of oṁkāra are described as follows:

oṁ ity ekākṣaraṁ brahma vyāharan mām anusmaran
yaḥ prayāti tyajan dehaṁ sa yāti paramāṁ gatim

This verse indicates that oṁkāra, or praṇava, is a direct representation of the Supreme Personality of Godhead. Therefore if at the time of death one simply remembers oṁkāra, he remembers the Supreme Personality of Godhead and is therefore immediately transferred to the spiritual world. Oṁkāra is the basic principle of all Vedic mantras, for it is a representation of Lord Kṛṣṇa, understanding of whom is the ultimate goal of the Vedas, as stated in the Bhagavad-gītā (vedaiś ca sarvair aham eva vedyaḥ). Māyāvādī philosophers cannot understand these simple facts explained in the Bhagavad-gītā, and yet they are very proud of being Vedāntīs. Sometimes, therefore, we refer to the Vedāntī philosophers as Vidantīs, those who have no teeth (vi means “without,” and dantī means “possessing teeth”). The statements of the Śaṅkara philosophy, which are the teeth of the Māyāvādī philosopher, are always broken by the strong arguments of Vaiṣṇava philosophers such as the great ācāryas, especially Rāmānujācārya. Śrīpāda Rāmānujācārya and Madhvācārya break the teeth of the Māyāvādī philosophers, who can therefore be called Vidantīs, “toothless.”

As mentioned above, the transcendental vibration oṁkāra is explained in the Bhagavad-gītā, chapter Eight, verse thirteen:

oṁ ity ekākṣaraṁ brahma vyāharan mām anusmaran
yaḥ prayāti tyajan dehaṁ sa yāti paramāṁ gatim

“After being situated in this yoga practice and vibrating the sacred syllable oṁ, the supreme combination of letters, if one thinks of the Supreme Personality of Godhead and quits his body, he will certainly reach the spiritual planets.” If one actually understands that oṁkāra is the sound representation of the Supreme Personality of Godhead, whether he chants oṁkāra or the Hare Kṛṣṇa mantra, the result is certainly the same.

The transcendental vibration of oṁkāra is further explained in the Bhagavad-gītā, chapter Nine, verse seventeen:

pitāham asya jagato mātā dhātā pitāmahaḥ
vedyaṁ pavitram oṁkāra ṛk sāma yajur eva ca

“I am the father of this universe, the mother, the support and the grandsire. I am the object of knowledge, the purifier and the syllable oṁ. I am also the Ṛg, the Sāma and the Yajur Vedas.”

Similarly, the transcendental sound oṁ is further explained in the Bhagavad-gītā, chapter Seventeen, verse twenty-three:

oṁ tat sad iti nirdeśo brahmaṇas tri-vidhaḥ smṛtaḥ
brāhmaṇās tena vedāś ca yajñāś ca vihitāḥ purā

“From the beginning of creation, the three syllables oṁ tat sat have been used to indicate the Supreme Absolute Truth [Brahman]. They were uttered by brāhmaṇas while chanting Vedic hymns and during sacrifices for the satisfaction of the Supreme.”

Throughout all the Vedic literatures the glories of oṁkāra are specifically mentioned. Śrīla Jīva Gosvāmī, in his thesis Bhagavat-sandarbha, says that in the Vedic literature oṁkāra is considered to be the sound vibration of the holy name of the Supreme Personality of Godhead. Only this vibration of transcendental sound can deliver a conditioned soul from the clutches of māyā. Sometimes oṁkāra is also called the deliverer (tāra). Śrīmad-Bhāgavatam begins with the oṁkāra vibration: oṁ namo bhagavate vāsudevāya. Therefore oṁkāra has been described by the great commentator Śrīdhara Svāmī as tārāṅkura, the seed of deliverance from the material world. Since the Supreme Godhead is absolute, His holy name and His sound vibration oṁkāra are as good as He Himself. Caitanya Mahāprabhu says that the holy name, or oṁkāra, the transcendental representation of the Supreme Personality of Godhead, has all the potencies of the Personality of Godhead.

nāmnām akāri bahudhā nija-sarva-śaktis
 tatrārpitā niyamitaḥ smaraṇe na kālaḥ

All potencies are invested in the holy vibration of the holy name of the Lord. There is no doubt that the holy name of the Lord, or oṁkāra, is the Supreme Personality of Godhead Himself. In other words, anyone who chants oṁkāra and the holy name of the Lord, Hare Kṛṣṇa, immediately meets the Supreme Lord directly in His sound form. In the Nārada-pañcarātra it is clearly said that the Supreme Personality of Godhead Nārāyaṇa personally appears before the chanter who engages in chanting the aṣṭākṣara, or eight-syllable mantra, oṁ namo nārāyaṇāya. A similar statement in the Māṇḍūkya Upaniṣad declares that whatever one sees in the spiritual world is all an expansion of the spiritual potency of oṁkāra.

On the basis of all the Upaniṣads, Śrīla Jīva Gosvāmī says that oṁkāra is the Supreme Absolute Truth and is accepted as such by all the ācāryas and authorities. Oṁkāra is beginningless, changeless, supreme and free from deterioration and external contamination. Oṁkāra is the origin, middle and end of everything, and any living entity who thus understands oṁkāra attains the perfection of spiritual identity in oṁkāra. Oṁkāra, being situated in everyone’s heart, is īśvara, the Supreme Personality of Godhead, as confirmed in the Bhagavad-gītā (18.61): īśvaraḥ sarva-bhūtānāṁ hṛd-deśe ’rjuna tiṣṭhati. Oṁkāra is as good as Viṣṇu because oṁkāra is as all-pervasive as Viṣṇu. One who knows oṁkāra and Lord Viṣṇu to be identical no longer has to lament or hanker. One who chants oṁkāra no longer remains a śūdra but immediately comes to the position of a brāhmaṇa. Simply by chanting oṁkāra one can understand the whole creation to be one unit, or an expansion of the energy of the Supreme Lord: idaṁ hi viśvaṁ bhagavān ivetaro yato jagat-sthāna-nirodha-sambhavāḥ. “The Supreme Lord Personality of Godhead is Himself this cosmos, and still He is aloof from it. From Him only this cosmic manifestation has emanated, in Him it rests, and unto Him it enters after annihilation.” (Bhāg. 1.5.20) Although one who does not understand concludes otherwise, Śrīmad-Bhāgavatam states that the entire cosmic manifestation is but an expansion of the energy of the Supreme Lord. Realization of this is possible simply by chanting the holy name of the Lord, oṁkāra.

One should not, however, foolishly conclude that because the Supreme Personality of Godhead is omnipotent, we have manufactured a combination of letters — a, u and m — to represent Him. Factually the transcendental sound oṁkāra, although a combination of the three letters a, u and m, has transcendental potency, and one who chants oṁkāra will very soon realize oṁkāra and Lord Viṣṇu to be nondifferent. Kṛṣṇa declares, praṇavaḥ sarva-vedeṣu: “I am the syllable oṁ in the Vedic mantras.” (Bg. 7.8) One should therefore conclude that among the many incarnations of the Supreme Personality of Godhead, oṁkāra is the sound incarnation. All the Vedas accept this thesis. One should always remember that the holy name of the Lord and the Lord Himself are always identical (abhinnatvān nāma-nāminoḥ). Since oṁkāra is the basic principle of all Vedic knowledge, it is uttered before one begins to chant any Vedic hymn. Without oṁkāra, no Vedic mantra is successful. The Gosvāmīs therefore declare that praṇava (oṁkāra) is the complete representation of the Supreme Personality of Godhead, and they have analyzed oṁkāra in terms of its alphabetical constituents as follows:

a-kāreṇocyate kṛṣṇaḥ sarva-lokaika-nāyakaḥ
u-kāreṇocyate rādhā ma-kāro jīva-vācakaḥ

Oṁkāra is a combination of the letters a, u and m. A-kāreṇocyate kṛṣṇaḥ: the letter a (a-kāra) refers to Kṛṣṇa, who is sarva-lokaika-nāyakaḥ, the master of all living entities and planets, material and spiritual. Nāyaka means “leader.” He is the supreme leader (nityo nityānāṁ cetanaś cetanānām). The letter u (u-kāra) indicates Śrīmatī Rādhārāṇī, the pleasure potency of Kṛṣṇa, and m (ma-kāra) indicates the living entities (jīvas). Thus oṁ is the complete combination of Kṛṣṇa, His potency and His eternal servitors. In other words, oṁkāra represents Kṛṣṇa, His name, fame, pastimes, entourage, expansions, devotees, potencies and everything else pertaining to Him. As Caitanya Mahāprabhu states in the present verse of Śrī Caitanya-caritāmṛta, sarva-viśva-dhāma: oṁkāra is the resting place of everything, just as Kṛṣṇa is the resting place of everything (brahmaṇo hi pratiṣṭhāham).

The Māyāvādī philosophers consider many Vedic mantras to be the mahā-vākya, or principal Vedic mantra, such as tat tvam asi (Chāndogya Upaniṣad 6.8.7), idaṁ sarvaṁ yad ayam ātmā and brahmedaṁ sarvam (Bṛhad-āraṇyaka Upaniṣad 2.5.1), ātmaivedaṁ sarvam (Chāndogya Upaniṣad 7.25.2) and neha nānāsti kiñcana (Kaṭha Upaniṣad 2.1.11). That is a great mistake. Only oṁkāra is the mahā-vākya. All these other mantras that the Māyāvādīs accept as the mahā-vākya are only incidental. They cannot be taken as the mahā-vākya, or mahā-mantra. The mantra tat tvam asi indicates only a partial understanding of the Vedas, unlike oṁkāra, which represents the full understanding of the Vedas. Therefore the transcendental sound that includes all Vedic knowledge is oṁkāra (praṇava).

Aside from oṁkāra, none of the words uttered by the followers of Śaṅkarācārya can be considered the mahā-vākya. They are merely passing remarks. Śaṅkarācārya, however, has never stressed chanting of the mahā-vākya oṁkāra; he has accepted only tat tvam asi as the mahā-vākya. Imagining the living entity to be God, he has misrepresented all the mantras of the Vedānta-sūtra with the motive of proving that there is no separate existence of the living entities and the Supreme Absolute Truth. This is similar to the politician’s attempt to prove nonviolence from the Bhagavad-gītā. Kṛṣṇa is violent to demons, and to attempt to prove that Kṛṣṇa is not violent is ultimately to deny Kṛṣṇa. As such explanations of the Bhagavad-gītā are absurd, so also is Śaṅkarācārya’s explanation of the Vedānta-sūtra, and no sane and reasonable man will accept it. At present, however, the Vedānta-sūtra is misrepresented not only by the so-called Vedāntīs but also by other unscrupulous persons who are so degraded that they even recommend that sannyāsīs eat meat, fish and eggs. In this way, the so-called followers of Śaṅkara, the impersonalist Māyāvādīs, are sinking lower and lower. How can these degraded men explain the Vedānta-sūtra, which is the essence of all Vedic literature?

Lord Śrī Caitanya Mahāprabhu has declared, māyāvādi-bhāṣya śunile haya sarva-nāśa: “Anyone who hears commentary on the Vedānta-sūtra from the Māyāvāda school is completely doomed.” As explained in the Bhagavad-gītā (15.15), vedaiś ca sarvair aham eva vedyaḥ: all Vedic literature aims at understanding Kṛṣṇa. Māyāvāda philosophy, however, has deviated everyone from Kṛṣṇa. Therefore there is a great need for the Kṛṣṇa consciousness movement all over the world to save the world from degradation. Every intelligent and sane man must abandon the philosophical explanation of the Māyāvādīs and accept the explanation of Vaiṣṇava ācāryas. One should read Bhagavad-gītā As It Is to try to understand the real purport of the Vedas.