His Divine Grace A.C. Bhaktivedanta Swami Prabhupāda showed an excellent example of ekānta-bhakti, single-minded devotion to the Supreme Lord. Prabhupāda showed this in many ways. For example, his commentary on Śrī Kṛṣṇa's book, Bhagavad-gītā, does not even slightly deviate from Kṛṣṇa's true intent. Impersonalism taints the vast majority of Bhagavad-gītā commentaries, but Śrīla Prabhupāda's purports in Bhagavad-gītā As It Is lead the reader directly to the lotus feet of Kṛṣṇa. This is true of all of Prabhupāda's books—Śrīmad-Bhāgavatam, Caitanya-caritāmṛta, and so on. His translation of the Sanskrit or Bengali is always accurate from a scholarly point of view, but at the same time he writes as a pure devotee: "Surrender to Kṛṣṇa."
In all of Śrīla Prabhupāda's spontaneous conversations, he was single-mindedly Kṛṣṇa conscious. When he spoke of Kṛṣṇa, he seemed to be talking about his dearmost friend, not merely repeating something he had read. Sometimes his kṛṣṇa-kathā took the form of convincing an atheist scientist that there is a supreme controller, sometimes he related the pastimes of Kṛṣṇa to his disciples, and sometimes he assured devotees that Kṛṣṇa is in our hearts and will give us the intelligence to execute a difficult service. Śrīla Prabhupāda maintained this single-mindedness even while undergoing the rigors of constant travel and while living in the biggest cities of the world. Wherever he was, Prabhupāda was on a mission for Kṛṣṇa.
Being single-pointed in devotional service does not mean shutting out reality. Exclusivity can become sectarian if one focuses on relative truths or dedicates oneself to an ordinary person. But when the object of appreciation is the Supreme Personality of Godhead, one attains the broadest vision, the vision of a mahātmā.
The devotee who is fixed on Kṛṣṇa has actually attained to the complete truth. That the Lord is the complete truth is stated in the Invocation to the Īśopaniṣad: oṁ pūrṇam adaḥ pūrṇam idam [Īśopaniṣad, Invocation]. "The Personality of Godhead is perfect and complete." A devotee glorifies the Lord as the complete Absolute Truth when he utters the famous Vedic aphorism tat tvam asi, "You are that." The impersonalist philosophers adore the tat tvam asi aphorism because they take it to mean that they are one with the formless Brahman. But the actual meaning of tat tvam asi is different. When the devotee says "You are that," he is addressing the Supreme Lord. Śrīla Prabhupāda explains in his purport to Bhagavad-gītā 4.9:
The Vedic version tat tvam asi is actually applied in this case. Anyone who understands Lord Kṛṣṇa to be the Supreme, or who says unto the Lord, "You are the same Supreme Brahman, the Personality of Godhead," is certainly liberated instantly, and consequently his entrance into the transcendental association of the Lord is guaranteed.
A pure devotee who sees Kṛṣṇa in everything can maintain one-pointed concentration on the Lord, even while performing a wide variety of services for Him. By contrast, materialistic persons cannot be ekāntī, or focused. Because the field of sense gratification tempts the conditioned souls in many directions, and because the mind is very fickle, the hedonist's attention is splayed. As Lord Kṛṣṇa says,
vyavasāyātmikā buddhir ekeha kuru-nandana
bahu-śākhā hy anantāś ca buddhayo 'vyavasāyinām
"Those who are on this path are resolute in purpose, and their aim is one. O beloved child of the Kurus, the intelligence of those who are irresolute is many-branched" (Bg. 2.41).
Śukadeva Gosvāmī describes the materialist in a similar way in the Śrīmad-Bhāgavatam (2.1.2):
śrotavyādīni rājendra nṛṇāṁ santi sahasraśaḥ
apaśyatām ātma-tattvaṁ gṛheṣu gṛha-medhinām
"Those persons who are materially engrossed, being blind to the knowledge of ultimate truth, have many subject matters for hearing in human society, O emperor." Absorbed in political work or scientific research or social and economic betterment, the gṛhamedhīs put aside the ultimate problems of old age, disease, and death. They do not inquire about self-realization, which would lead them eventually to Kṛṣṇa consciousness. But a person who wants to succeed in bhakti must give up the life of bewildering distractions and take up devotional service under the guidance of a spiritual master.
The best way to cultivate single-minded devotion to Kṛṣṇa is to chant the Hare Kṛṣṇa mantra. This practice is what the scriptures and ācāryas recommend as the main limb of devotional service for the Age of Kali. By this one simple act—chanting and hearing the holy name—we serve Lord Kṛṣṇa the way He likes best. Haridāsa Ṭhākura set the example by making the chanting of hari-nāma his exclusive service. Serious Gauḍīya Vaiṣṇavas follow in his footsteps by chanting daily at least sixteen rounds of Hare Kṛṣṇa on beads. As stated in the Caitanya-caritāmṛta (Antya 3.268), "The holy name of Kṛṣṇa is so attractive that anyone who chants it—including all living entities, moving and unmoving, and even Lord Kṛṣṇa Himself—becomes imbued with love of Kṛṣṇa. This is the effect of chanting the Hare Kṛṣṇa mantra."
In the beginning stages, the restless mind balks at the single-minded devotion required to chant Hare Kṛṣṇa for long stretches. The holy name is actually the sweetest nectar, but until we reach the spontaneous stage of devotion, one has to outsmart the mischievous mind. The mind is called cañcala, or unfaithful, but it can become the devotee's best friend. When one chants Hare Kṛṣṇa and performs other duties with concentration and devotion, the mind clears and the devotee realizes his true interest. Then the devotee becomes attracted to serving the holy names in the ekāntina spirit, which Nārada Muni recommends here as the best.