The chanting of “pranava omkar” or “om” is very popular because all the Vedic mantras start from it. Krishna says in the Bhagavad gita (7.8) that “I am the pranava, the syllable Om, which is the principal word in the Vedas.” Pranava omkar is considered the sound incarnation of God and thus is non-different from Him. Further, in the Bhagavad gita (8.13), Krishna states, “One who at the time of death, leaves his body, chanting the syllable ‘Om’ and thinking of Me, attains my supreme abode.” It is also mentioned in the Bhagavad gita (17.24) that the transcendentalists begin all activities of sacrifice, penance, and charity by chanting the transcendental sound Om.
Considering the above facts, it is very reasonable when people ask that why does the Hare Krishna Revolution stress the chanting of the Hare Krishna mahamantra, when Om is also non-different than Krishna? If one chants “Om” considering it to be non-different than Krishna, then there is no objection to the chanting of Om because one will remember Krishna while chanting it. However when someone thinks Om to be different than Krishna, then one is in ignorance. Such men either consider it to be impersonal aspect of God or separately powerful of Krishna. Om is neither the impersonal aspect of Krishna nor is it independent of Krishna.
People possessing such erroneous conceptions about Omkar, object to the chanting of the holy name of Krishna. If one is convinced that Krishna and Om are non-different then the question of Om’s superiority does not arise. A UN official, who came to meet His Divine Grace A.C. Bhaktivedanta Swami Prabhupada in Vrindavan, was stressing the importance of Om over Hare Krishna and argued that since all the Upanishads start from the pranava, the chanting of “Om” is more exalted.
Srila Prabhupada explained that the Upanishads are meant to take one nearer to God, or Krishna. However everyone cannot accept Krishna as God. As soon as Krishna is presented as God, the materialists have a problem, “Why should I accept Krishna as God?” Such people think that Krishna is an ordinary boy tending the cows and playing with His cowherd boyfriends in the forest of Vrindavan. On the other hand, the yogis and the impersonalists think that Krishna is the impersonal Brahman, who has assumed a human form.
Since those who are envious of Krishna, have problems in accepting Krishna as the Supreme Personality of Godhead, the Upanishads recommend the chanting of Om to such people. Since Om is non-different than Krishna, the Upanishads bring such people near to Krishna in an indirect way. The study of Upanishads is meant for the neophytes, who cannot chant Krishna’s direct names. The neophytes object to the name of Krishna but since they have no objections to Om, the Upanishads recommend the chanting of Om, which is the sound form of Krishna.
It is not very easy to chant the holy name of Krishna. The Bhagavad gita, also known as the Geetopanishad, or the essence of all the Upanishads, says that one who is cleansed of all sinful reaction can worship Krishna with determination (7.28). In other words, a sinful person cannot chant the holy name of Krishna. The merciless hunter Valmiki, who was advised to chant rāma by Narada Muni, was unable to do so because of excessive sins.
The Upanishads, however want to engage everyone in the chanting of the holy names of Krishna because one can one attain supreme bliss only when one chants them. Therefore, the Upanishads trick those, who cannot chant the direct names of God like Krishna, Govinda and Hari into the chanting of Om. Yena tena prakarena manah krsne nivesayet: somehow or the other, one should engage the mind in Krishna. Since Om is not a direct name of Krishna, the yogis, jnanis and the materialists (karmis) have no problems in chanting it. However, by the regular chanting of the pranava, they will get cleansed of their sinful reactions and gradually rise to the point of chanting the direct names of Krishna such as Hare Krishna Hare Krishna, Krishna Krishna Hare Hare/ Hare Rama Hare Rama, Rama Rama Hare Hare.
Thus, it is the aim of the Upanishads that everyone should chant Hare Krishna and hence they are bringing all and sundry near to Krishna indirectly.
When one chants Hare Krishna, one gets the benefit of chanting Om but when one chants Om independently of Krishna consciousness, one remains bereft of the variegated spiritual relationships (rasa) that one realises by chanting the Hare Krishna mahamantra. Therefore the Hare Krishna mantra is known as mahamantra, which means that there is no mantra superior to it, including Om.