There are many Vedic references which specifically recommend the chanting of the Hare Krishna maha-mantra as the most effective and advantageous means of reaching spiritual realization and counteracting all the problems of this age. Some of these verses are the following:
These sixteen words--Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/Hare Rama, Hare Rama, Rama Rama, Hare Hare--are especially meant for counteracting the ill effects of the present age of quarrel and anxiety. (Kali-santarana Upanishad)
All mantras and all processes for self-realization are compressed into the Hare Krishna maha-mantra. (Narada-pancaratra)
Chant the holy names, chant the holy names, chant the holy names. In this age of Kali [the age of quarrel and confusion] without a doubt there is no other way, there is no other way, there is no other way. (Brihan-naradiya Purana 38.126)
In this age there is no use in meditation, sacrifice and temple worship. Simply by chanting the holy name of Krishna--Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/Hare Rama, Hare Rama, Rama Rama, Hare Hare--one can achieve perfect self-realization. (Vishnu Purana 6.2.17)
The self-realization which was achieved in the Satya millennium by meditation, in the Treta millennium by the performance of different sacrifices, and in the Dvapara millennium by worship of Lord Krishna [as the Deity in the temple], can be achieved in the age of Kali simply by chanting the holy names, Hare Krishna. (Bhag.12.3.52) (Verses similar to this are also found in the Padma Purana, Uttara-khanda 72.25, and the Brihan-naradiya Purana 38.97)
Living beings who are entangled in the complicated meshes of birth and death can be freed immediately by even unconsciously chanting the holy name of Krishna, which is feared by fear personified. (Bhag.1.1.14)
When instructing King Pariksit, the great sage Sri Shukadeva Gosvami said, "O King, constant chanting of the holy name of the Lord after the ways of the great authorities is the doubtless and fearless way of success for all, including those who are free from all material desires, those who are desirous of all material enjoyment, and also those who are self-satisfied by dint of transcendental knowledge. What is the value of a prolonged life which is wasted, inexperienced by years in this world? Better a moment of full consciousness, because that gives one a start in searching after his supreme interest." (Bhag.2.1.11-13)
The reason that chanting the Lord's names is such an effective process is because the Lord and His names are identical: they are the same spiritual energy. By chanting Hare Krishna we are in immediate contact with God. If we chant someone else's name, we cannot enjoy their association because the name and the person are different. For example, by chanting "water, water, water," we do not quench our thirst because water and the name are two different things. But in the spiritual world everything is absolute. Krishna is nondifferent from His names and, therefore, we can feel His presence simply by chanting His names. This is further elaborated in the Caitanya-caritamrta (Madhya-lila, 17.131-133), which explains that there is no difference between the Lord's name, form, or personality, and they are all transcendentally sweet. Krishna's name is the same as Krishna Himself, and is not material in any way. It gives spiritual benedictions and is full of pleasure. But in the material world everything is different. Furthermore, in Caitanya-cartamrta (Adi-lila, 17.22, and the Padma Purana), the Hare Krishna maha-mantra is said to be the sound incarnation of Krishna, and anyone who chants this mantra is in direct association with Krishna and is delivered from the clutches of the material energy.
It is explained that because chanting the names of God brings us in direct contact with God in proportion to the chanter's purity, this process of self-realization is the way of success for everyone. The Bhagavatam (2.1.11) discloses that the chanting of God's names in the manner of the great authorities is the doubtless way to spiritual success for everyone, no matter whether they are full of material desires or free of all desires or self-satisfied because of their spiritual knowledge.
Simply by relying on the chanting of the holy names of God, one need not depend upon other processes, rituals, paraphernalia, or persons. One does not even have to be initiated by a spiritual master to chant the maha-mantra. As the Caitanya-caritamrta (Madhya-lila, 15.108) says, one does not have to take initiation, but only has to chant the holy names. Thus, deliverance is available to even the lowest of people. Furthermore, Rupa Gosvami writes about the potency of the holy name in his Padyavali:
The holy name of Lord Krishna is an attractive feature for many saintly, liberal people. It is the annihilator of all sinful reactions and is so powerful that save for the dumb who cannot chant it, it is readily available to everyone, including the lowest type of man, the chandala. The holy name of Krishna is the controller of the opulence of liberation, and it is identical with Krishna. Simply by touching the holy name with one's tongue, immediate effects are produced. Chanting the holy name does not depend on initiation, pious activities or thepurascarya regulative principles generally observed before initiation. The holy name does not wait for all these activities. It is self-sufficient. (Padyavali 29)
The name of the Lord need not be chanted with regard to place, time, circumstantial conditions, preliminary self-purification or any other factors. Rather, it is completely independent of all other processes and rewards all the desires of those who eagerly chant it. (Skanda Purana)
Therefore, without a doubt, the Hare Krishna mantra is the most potent mantra one can utilize for spiritual upliftment. The Caitanya-caritamrta (Madhya-lila, 15.107) also points out that one is freed of all sinful reactions simply by chanting Krishna's names. And all the nine types of devotional service are completed by this process. Thus, in Kali-yuga only the chanting of the holy names is necessary for worshiping the Lord. However, if one is not able to chant purely or follow the regulations for chanting, it is recommended that one get further guidance from a bona fide spiritual master.
"The names of the Supreme Lord who has the disc as His weapon should be glorified always and everywhere." (Vaisakha-mahatmya section of the Padma Purana) But since the age of Kali is the most difficult, where men have short durations of life, it is also the most fortunate age. This is explained in Srimad-Bhagavatam (11.5.36-37 and 12.3.51) which states that those who are wise know the value of this age of Kali because, in spite of the fallen nature of this age, the spiritual perfection of life can be attained by the easy process of sankirtana, the congregational chanting of Krishna's holy names. No better position can be found to attain freedom from material existence and entrance into the spiritual kingdom than joining the Lord's sankirtana movement.
Even those living in other ages desire to take birth in Kali-yuga to take advantage of this special concession of a speedy delivery from the cycle of birth and death through the process of sankirtana. This is confirmed in Srimad-Bhagavatam (11.5.38) where we find it said that those who live during Satya-yuga and other ages wish to be born in Kali-yuga just to take advantage of associating with the devotees of Lord Narayana, who are especially found in South India.
The Srimad-Bhagavatam (11.5.32) explains that intelligent persons perform congregational singing of Krishna's names to worship the incarnation of Krishna who sings His own names, and who is accompanied by His associates and confidential companions. Therefore, as the Caitanya-caritamrta (Adi-lila, 7.74) specifically says, the essence of all scriptural teachings is that the only religious principle in the age of Kali is to chant the Lord's holy names, which are the basis of all Vedic hymns. "In this way the most perfect penance to be executed in this world is the chanting of the name of Lord Sri Hari. Especially in the age of Kali, one can satisfy the Supreme Lord Vishnu by performing sankirtana." (Caturmasya-mahatmya section of the Skanda Purana)
The fact of the matter, as explained in Srimad-Bhagavatam (3.33.6-7), is that regardless of what one's present situation is, if a person once speaks about the activities and chants the holy names of the Supreme, or hears about and remembers Him, he becomes eligible to engage in the Vedic rituals. And how much more glorious are those who regularly chant the holy names. Such people are indeed worshipable, for they must have performed all kinds of austerities, achieved the characteristics of the Aryans, studied the Vedas, bathed at all the holy places of pilgrimage, and done whatever else is required.