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SB 10.1.4

nivṛtta-tarṣair upagīyamānād
 bhavauṣadhāc chrotra-mano-’bhirāmāt
ka uttamaśloka-guṇānuvādāt
 pumān virajyeta vinā paśughnāt
Synonyms: 
nivṛtta — released from; tarṣaiḥ — lust or material activities; upagīyamānāt — which is described or sung; bhava-auṣadhāt — which is the right medicine for the material disease; śrotra — the process of aural reception; manaḥ — the subject matter of thought for the mind; abhirāmāt — from the pleasing vibrations from such glorification; kaḥ — who; uttamaśloka — of the Supreme Personality of Godhead; guṇa-anuvādāt — from describing such activities; pumān — a person; virajyeta — can keep himself aloof; vinā — except; paśu-ghnāt — either a butcher or one who is killing his own personal existence.
Translation: 
Glorification of the Supreme Personality of Godhead is performed in the paramparā system, that is, it is conveyed from the spiritual master to disciple. Such glorification is relished by those no longer interested in the false, temporary glorification of this cosmic manifestation. Descriptions of the Lord are the right medicine for the conditioned soul undergoing repeated birth and death. Therefore, who will cease hearing such glorification of the Lord except a butcher or one who is killing his own self?
Purport: 

In India it is the practice among the general populace to hear about Kṛṣṇa, either from Bhagavad-gītā or from Śrīmad-Bhāgavatam, in order to gain relief from the disease of repeated birth and death. Although India is now fallen, when there is a message that someone will speak about Bhagavad-gītā or Śrīmad-Bhāgavatam, thousands of people still gather to hear. This verse indicates, however, that such recitation of Bhagavad-gītā and Śrīmad-Bhāgavatam must be done by persons completely freed from material desires (nivṛtta-tarṣaiḥ). Everyone within this material world, beginning from Brahmā down to the insignificant ant, is full of material desires for sense enjoyment, and everyone is busy in sense gratification, but when thus engaged one cannot fully understand the value of kṛṣṇa-kathā, either in the form of Bhagavad-gītā or in Śrīmad-Bhāgavatam.

If we hear the glories of the Supreme Personality of Godhead from liberated persons, this hearing will certainly free us from the bondage of material activities, but hearing Śrīmad-Bhāgavatam spoken by a professional reciter cannot actually help us achieve liberation. Kṛṣṇa-kathā is very simple. In Bhagavad-gītā it is said that Kṛṣṇa is the Supreme Personality of Godhead. As He Himself explains, mattaḥ parataraṁ nānyat kiñcid asti dhanañjaya: “O Arjuna, there is no truth superior to Me.” (Bg. 7.7) Simply by understanding this fact — that Kṛṣṇa is the Supreme Personality of Godhead — one can become a liberated person. But, especially in this age, because people are interested in hearing Bhagavad-gītā from unscrupulous persons who depart from the simple presentation of Bhagavad-gītā and distort it for their personal satisfaction, they fail to derive the real benefit. There are big scholars, politicians, philosophers and scientists who speak on Bhagavad-gītā in their own polluted way, and people in general hear from them, being uninterested in hearing the glories of the Supreme Personality of Godhead from a devotee. A devotee is one who has no other motive for reciting Bhagavad-gītā and Śrīmad-Bhāgavatam than to serve the Lord. Śrī Caitanya Mahāprabhu has therefore advised us to hear the glories of the Lord from a realized person (bhāgavata paro diya bhāgavata sthane). Unless one is personally a realized soul in the science of Kṛṣṇa consciousness, a neophyte should not approach him to hear about the Lord, for this is strictly forbidden by Śrīla Sanātana Gosvāmī, who quotes from the Padma Purāṇa:

avaiṣṇava-mukhodgīrṇaṁ
 pūtaṁ hari-kathāmṛtam
śravaṇaṁ naiva kartavyaṁ
 sarpocchiṣṭaṁ yathā payaḥ

One should avoid hearing from a person not situated in Vaiṣṇava behavior. A Vaiṣṇava is nivṛtta-tṛṣṇa; that is, he has no material purpose, for his only purpose is to preach Kṛṣṇa consciousness. So-called scholars, philosophers and politicians exploit the importance of Bhagavad-gītā by distorting its meaning for their own purposes. Therefore this verse warns that kṛṣṇa-kathā should be recited by a person who is nivṛtta-tṛṣṇa. Śukadeva Gosvāmī epitomizes the proper reciter for Śrīmad-Bhāgavatam, and Parīkṣit Mahārāja, who purposefully left his kingdom and family prior to meeting death, epitomizes the person fit to hear it. A qualified reciter of Śrīmad-Bhāgavatam gives the right medicine (bhavauṣadhi) for the conditioned souls. The Kṛṣṇa consciousness movement is therefore trying to train qualified preachers to recite Śrīmad-Bhāgavatam and Bhagavad-gītā throughout the entire world, so that people in general in all parts of the world may take advantage of this movement and thus be relieved of the threefold miseries of material existence.

The instructions of Bhagavad-gītā and the descriptions of Śrīmad-Bhāgavatam are so pleasing that almost anyone suffering from the threefold miseries of material existence will desire to hear the glories of the Lord from these books and thus benefit on the path of liberation. Two classes of men, however, will never be interested in hearing the message of Bhagavad-gītā and Śrīmad-Bhāgavatam — those who are determined to commit suicide and those determined to kill cows and other animals for the satisfaction of their own tongues. Although such persons may make a show of hearing Śrīmad-Bhāgavatam at a Bhāgavata-saptāha, this is but another creation of the karmīs, who cannot derive any benefit from such a performance. The word paśu-ghnāt is important in this connection. Paśu-ghna means “butcher.” Persons fond of performing ritualistic ceremonies for elevation to the higher planetary systems must offer sacrifices (yajñas) by killing animals. Lord Buddhadeva therefore rejected the authority of the Vedas because his mission was to stop animal sacrifices, which are recommended in Vedic ritualistic ceremonies

nindasi yajña-vidher ahaha śruti-jātaṁ
sa-daya-hṛdaya darśita-paśu-ghātaṁ
keśava dhṛta-buddha-śarīra jaya jagadīśa hare

(Gīta-govinda)

Even though animal sacrifices are sanctioned in Vedic ceremonies, men who kill animals for such ceremonies are considered butchers. Butchers cannot be interested in Kṛṣṇa consciousness, for they are already materially allured. Their only interest lies in developing comforts for the temporary body.

bhogaiśvarya-prasaktānāṁ
 tayāpahṛta-cetasām
vyavasāyātmikā buddhiḥ
 samādhau na vidhīyate

“In the minds of those who are too attached to sense enjoyment and material opulence, and who are bewildered by such things, the resolute determination of devotional service to the Supreme Lord does not take place.” (Bg. 2.44) Śrīla Narottama dāsa Ṭhākura says:

manuṣya-janama pāiyā, rādhā-kṛṣṇa nā bhajiyā,
 jāniyā śuniyā viṣa khāinu

Anyone who is not Kṛṣṇa conscious and who therefore does not engage in the service of the Lord is also paśu-ghna, for he is willingly drinking poison. Such a person cannot be interested in kṛṣṇa-kathā because he still has a desire for material sense gratification; he is not nivṛtta-tṛṣṇa. As it is said, traivargikās te puruṣā vimukhā hari-medhasaḥ. Those interested in trivarga — that is, in dharma, artha and kāma — are religious for the sake of achieving a material position with which to gain better facilities for sense gratification. Such persons are killing themselves by willingly keeping themselves in the cycle of birth and death. They cannot be interested in Kṛṣṇa consciousness.

For kṛṣṇa-kathā, topics about Kṛṣṇa consciousness, there must be a speaker and a hearer, both of whom can be interested in Kṛṣṇa consciousness if they are no longer interested in material topics. One can actually see how this attitude automatically develops in persons who are Kṛṣṇa conscious. Although the devotees of the Kṛṣṇa consciousness movement are quite young men, they no longer read materialistic newspapers, magazines and so on, for they are no longer interested in such topics (nivṛtta-tarṣaiḥ). They completely give up the bodily understanding of life. For topics concerning Uttamaśloka, the Supreme Personality of Godhead, the spiritual master speaks, and the disciple hears with attention. Unless both of them are free from material desires, they cannot be interested in topics of Kṛṣṇa consciousness. The spiritual master and disciple do not need to understand anything more than Kṛṣṇa because simply by understanding Kṛṣṇa and talking about Kṛṣṇa, one becomes a perfectly learned person (yasmin vijñāte sarvam evaṁ vijñātaṁ bhavati, Muṇḍaka Upaniṣad 1.3). The Lord sits within everyone’s heart, and by the grace of the Lord the devotee receives instructions directly from the Lord Himself, who says in Bhagavad-gītā (15.15):

sarvasya cāhaṁ hṛdi sanniviṣṭo
 mattaḥ smṛtir jñānam apohanaṁ ca
vedaiś ca sarvair aham eva vedyo
 vedānta-kṛd veda-vid eva cāham

“I am seated in everyone’s heart, and from Me come remembrance, knowledge and forgetfulness. By all the Vedas, I am to be known; indeed, I am the compiler of Vedānta, and I am the knower of the Vedas.” Kṛṣṇa consciousness is so exalted that one who is perfectly situated in Kṛṣṇa consciousness, under the direction of the spiritual master, is fully satisfied by reading kṛṣṇa-kathā as found in Śrīmad-Bhāgavatam, Bhagavad-gītā and similar Vedic literatures. Since merely talking about Kṛṣṇa is so pleasing, we can simply imagine how pleasing it is to render service to Kṛṣṇa.

When discourses on kṛṣṇa-kathā take place between a liberated spiritual master and his disciple, others also sometimes take advantage of hearing these topics and also benefit. These topics are the medicine to stop the repetition of birth and death. The cycle of repeated birth and death, by which one takes on different bodies again and again, is called bhava or bhava-roga. If anyone, willingly or unwillingly, hears kṛṣṇa-kathā, his bhava-roga, the disease of birth and death, will certainly stop. Therefore kṛṣṇa-kathā is called bhavauṣadha, the remedy to stop the repetition of birth and death. Karmīs, or persons attached to material sense enjoyment, generally cannot give up their material desires, but kṛṣṇa-kathā is such a potent medicine that if one is induced to hear kṛṣṇa-kīrtana, he will certainly be freed from this disease. A practical example is Dhruva Mahārāja, who at the end of his tapasya was fully satisfied. When the Lord wanted to give Dhruva a benediction, Dhruva refused it. Svāmin kṛtārtho ’smi varaṁ na yāce. “My dear Lord,” he said, “I am fully satisfied. I do not ask for any benediction for material sense gratification.” We actually see that even young boys and girls in the Kṛṣṇa consciousness movement have given up their long practice of bad habits like illicit sex, meat-eating, intoxication and gambling. Because Kṛṣṇa consciousness is so potent that it gives them full satisfaction, they are no longer interested in material sense gratification.