CC Ādi 7.76

harer nāma harer nāma
harer nāmaiva kevalam
kalau nāsty eva nāsty eva
nāsty eva gatir anyathā
Word for word: 
hareḥ nāma — the holy name of the Lord; hareḥ nāma — the holy name of the Lord; hareḥ nāma — the holy name of the Lord; eva — certainly; kevalam — only; kalau — in this Age of Kali; na asti — there is none; eva — certainly; na asti — there is none; eva — certainly; na asti — there is none; eva — certainly; gatiḥ — progress; anyathā — otherwise.
Translation: 
“ ‘For spiritual progress in this Age of Kali, there is no alternative, there is no alternative, there is no alternative to the holy name, the holy name, the holy name of the Lord.’
Purport: 

For progress in spiritual life, the śāstras recommend meditation in Satya-yuga, sacrifice for the satisfaction of Lord Viṣṇu in Tretā-yuga and gorgeous worship of the Lord in the temple in Dvāpara-yuga, but in the Age of Kali one can achieve spiritual progress only by chanting the holy name of the Lord. This is confirmed in various scriptures. In Śrīmad-Bhāgavatam there are many references to this fact. In the Twelfth Canto (3.51) it is said:

kaler doṣa-nidhe rājannasti hy eko mahān guṇaḥ
kīrtanād eva kṛṣṇasya
mukta-saṅgaḥ paraṁ vrajet

In the Age of Kali there are many faults, for people are subjected to many miserable conditions, yet in this age there is one great benediction — simply by chanting the Hare Kṛṣṇa mantra one can be freed from all material contamination and thus be elevated to the spiritual world. The Nārada-pañcarātra also praises the Hare Kṛṣṇa mahā-mantra as follows:

trayo vedāḥ ṣaḍ-aṅgānichandāṁsi vividhāḥ surāḥ
sarvam aṣṭākṣarāntaḥ-sthaṁ
yac cānyad api vāṅ-mayam
sarva-vedānta-sārārthaḥ
saṁsārārṇava-tāraṇaḥ

“The essence of all Vedic knowledge — comprehending the three kinds of Vedic activity [karma-kāṇḍa, jñāna-kāṇḍa and upāsanā-kāṇḍa], the chandas, or Vedic hymns, and the processes for satisfying the demigods — is included in the eight syllables Hare Kṛṣṇa, Hare Kṛṣṇa. This is the reality of all Vedānta. The chanting of the holy name is the only means to cross the ocean of nescience.” Similarly, the Kali-santaraṇa Upaniṣad states, “Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare — these sixteen names composed of thirty-two syllables are the only means to counteract the evil effects of Kali-yuga. In all the Vedas it is seen that to cross the ocean of nescience there is no alternative to the chanting of the holy name.” Similarly, Śrī Madhvācārya, while commenting upon the Muṇḍaka Upaniṣad, has quoted the following verse from the Nārāyaṇa-saṁhitā:

dvāparīyair janair viṣṇuḥpañcarātrais tu kevalaiḥ
kalau tu nāma-mātreṇa
pūjyate bhagavān hariḥ

“In Dvāpara-yuga one could satisfy Kṛṣṇa or Viṣṇu only by worshiping Him gorgeously according to the pāñcarātrikī system, but in the Age of Kali one can satisfy and worship the Supreme Personality of Godhead Hari simply by chanting the holy name.” In his Bhakti-sandarbha (text 284), Śrīla Jīva Gosvāmī strongly emphasizes the chanting of the holy name of the Lord as follows:

nanu bhagavan-nāmātmakā eva mantrāḥ, tatra viśeṣeṇa namaḥ-śabdādy-alaṅkṛtāḥ śrī-bhagavatā śrīmad-ṛṣibhiś cāhita-śakti-viśeṣāḥ, śrī-bhagavatā samam ātma-sambandha-viśeṣa-pratipādakāś ca tatra kevalāni śrī-bhagavan-nāmāny api nirapekṣāṇy eva parama-puruṣārtha-phala-paryanta-dāna-samarthāni tato mantreṣu nāmato ’py adhika-sāmarthye labdhe kathaṁ dīkṣādy-apekṣā. ucyate — yady api svarūpato nāsti, tathāpi prāyaḥ svabhāvato dehādi-sambandhena kadarya-śīlānāṁ vikṣipta-cittānāṁ janānāṁ tat-saṅkocī-karaṇāya śrīmad-ṛṣi-prabhṛtibhir atrārcana-mārge kvacit kvacit kācit kācin maryādā sthāpitāsti.

Śrīla Jīva Gosvāmī states that the substance of all the Vedic mantras is the chanting of the holy name of the Lord. Every mantra begins with the prefix nama oṁ and eventually addresses by name the Supreme Personality of Godhead. By the supreme will of the Lord there is a specific potency in each and every mantra chanted by great sages like Nārada Muni and other ṛṣis. Chanting the holy name of the Lord immediately renovates the transcendental relationship of the living being with the Supreme Lord.

To chant the holy name of the Lord, one need not depend upon other paraphernalia, for one can immediately get all the desired results of linking with the Supreme Personality of Godhead. It may therefore be questioned why there is a necessity for initiation or further spiritual activities in devotional service for one who engages in the chanting of the holy name of the Lord. The answer is that although it is correct that one who fully engages in chanting the holy name need not depend upon the process of initiation, generally a devotee is addicted to many abominable material habits due to material contamination from his previous life. In order to get quick relief from all these contaminations, it is required that one engage in the worship of the Lord in the temple. The worship of the Deity in the temple is essential to reduce one’s restlessness due to the contaminations of conditioned life. Thus Nārada, in his pāñcarātrikī-vidhi, and other great sages have sometimes stressed that since every conditioned soul has a bodily concept of life aimed at sense enjoyment, to restrict this sense enjoyment the rules and regulations for worshiping the Deity in the temple are essential. Śrīla Rūpa Gosvāmī has described that the holy name of the Lord can be chanted by liberated souls, but almost all the souls we have to initiate are conditioned. It is advised that one chant the holy name of the Lord without offenses and according to the regulative principles, yet due to their past bad habits they violate these rules and regulations. Thus the regulative principles for worship of the Deity are also simultaneously essential.