Generally, materialistic persons are after some name, fame and material gain, so if someone takes to Kṛṣṇa consciousness for these reasons, he will never be able to understand this philosophy. Such persons take to religious principles as a social decoration. They admit themselves into some cultural institution for the sake of name only, especially in this age. Such persons also cannot understand the philosophy of Kṛṣṇa consciousness. Even if one is not greedy for material possessions but is too attached to family life, he also cannot understand Kṛṣṇa consciousness. Superficially, such persons are not very greedy for material possessions, but they are too attached to wife, children and family improvement. When a person is not contaminated by the above-mentioned faults yet at the ultimate issue is not interested in the service of the Supreme Personality of Godhead, or if he is a nondevotee, he also cannot understand thephilosophy of Kṛṣṇa consciousness.
(Srimad Bhagavatam------3:32:40------purport).

The Supreme Personality of Godhead Śrī Kṛṣṇa has very elaborately described the constitution of the soul in the previous chapter, with a view to delivering His intimate friend Arjuna from the ocean of material grief. And the path of realization has been recommended: buddhi-yoga, or Kṛṣṇa consciousness. Sometimes Kṛṣṇa consciousness is misunderstood to be inertia, and one with such a misunderstanding often withdraws to a secluded place to become fully Kṛṣṇa conscious by chanting the holy name of Lord Kṛṣṇa. But without being trained in the philosophy of Kṛṣṇa consciousness, it is not advisable to chant the holy name of Kṛṣṇa in a secluded place, where one may acquire only cheap adoration from the innocent public. Arjuna also thought of Kṛṣṇa consciousness or buddhi-yoga, or intelligence in spiritual advancement of knowledge, as something like retirement from active life and the practice of penance and austerity at a secluded place. In other words, he wanted to skillfully avoid the fighting by using Kṛṣṇa consciousness as an excuse. But as a sincere student, he placed the matter before his master and questioned Kṛṣṇa as to his best course of action. In answer, Lord Kṛṣṇa elaborately explained karma-yoga, or work in Kṛṣṇa consciousness, in this Third Chapter.
(Bhagavad-Gita------3:1------purport).

As Kṛṣṇa says in Bhagavad-gītā (7.15):
na māṁ duṣkṛtino mūḍhāḥ
prapadyante narādhamāḥ
māyayāpahṛta-jṣānā
āsuraṁ bhāvam āśritāḥ
"Those miscreants who are grossly foolish, lowest among mankind, whose knowledge is stolen by illusion, and who partake of the atheistic nature of demons, do not surrender unto Me." One who has not surrendered to Kṛṣṇa does not know the true principle of religion; otherwise he would have surrendered.
The question posed by the Viṣṇudūtas was very suitable. One who represents someone else must fully know that person's mission. The devotees in the Kṛṣṇa consciousness movement must therefore be fully aware of the mission of Kṛṣṇa and Lord Caitanya; otherwise they will be considered foolish. All devotees, especially preachers, must know the philosophy of Kṛṣṇa consciousness so as not to be embarrassed and insulted when they preach.
(Srimad Bhagavatam------6:1:38------purport).

Actually, everyone should fear the so-called society, friendship and love for which he works so hard all day and night. As indicated by Bali Mahārāja by the words janād bhītaḥ, every devotee in Kṛṣṇa consciousness should always be afraid of the common man engaged in pursuing material prosperity. Such a person is described as pramatta, a madman chasing the will-o'-the-wisp. Such men do not know that after a hard struggle for life one must change his body, with no certainty of what kind of body he will receive next. Those who are completely established in Kṛṣṇa conscious philosophy and who therefore understand the aim of life will never take to the activities of the materialistic dog race. But if a sincere devotee somehow does fall down, the Lord corrects him and saves him from gliding down to the darkest region of hellish life.
adānta-gobhir viśatāṁ tamisraṁ
punaḥ punaś carvita-carvaṇānām
(S.B.7:5:30)
The materialistic way of life is nothing but the repeated chewing of that which has already been chewed. Although there is no profit in such a life, people are enamored of it because of uncontrolled senses. Nūnaṁ pramattaḥ kurute vikarma (S.B.5:5:4). Because of uncontrolled senses, people fully engage in sinful activities by which they get a body full of suffering. Bali Mahārāja appreciated how the Lord had saved him from such a bewildered life of ignorance. He therefore said that his intelligence had been stunned. Stabdha-matir na budhyate. He could not understand how the Supreme Personality of Godhead favors His devotees by forcibly stopping their materialistic activities.
(Srimad Bhagavatam------8:22:11------purport).

Śrīla Bhaktisiddhānta Sarasvatī Mahārāja says in this connection: "O living entities, simply engage yourselves in Kṛṣṇa consciousness. This is the message of Śrī Caitanya Mahāprabhu." Lord Caitanya preached this cult, instructing the philosophy of Kṛṣṇa consciousness in His eight verses, or Śikṣāṣṭaka, and He said, ihā haite sarva-siddhi haibe sabāra: "By chanting the Hare Kṛṣṇa mantra, one will get all perfection in life." Therefore one who does not show Him respect or cannot appreciate His mercy despite all these merciful gestures is an asura, or opponent of bona fide devotional service to Lord Viṣṇu, even though he may be very much exalted in human society. The word asura refers to one who is against devotional service to the Supreme Personality of Godhead, Viṣṇu. It should be noted that unless one worships Śrī Caitanya Mahāprabhu it is useless to become a devotee of Kṛṣṇa, and unless one worships Kṛṣṇa it is also useless to become a devotee of Śrī Caitanya Mahāprabhu. Such devotional service is to be understood to be a product of Kali-yuga. Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura remarks in this connection that atheist smārtas, or worshipers of the five kinds of demigods, worship Lord Viṣṇu for a little satisfaction in material success but have no respect for Śrī Caitanya Mahāprabhu. Thinking Him to be one of the ordinary living entities, they discriminate between Gaurasundara and Śrī Kṛṣṇa. Such understanding is also demoniac and is against the conclusion of the ācāryas. Such a conclusion is a product of Kali-yuga.
(Sri Caitanya Caritamrta------1:8:12------purport).

The Bhagavad-gītā is spoken by the Lord so that human society can be perfectly organized from all angles of vision—politically, socially, economically, philosophically and religiously. From any point of view, human society can be reformed by the Kṛṣṇa consciousness movement; therefore one who spreads this philosophy of Kṛṣṇa consciousness for the benefit of all conditioned souls in the universe is perfect in pure devotional service.
(Sri Caitanya Caritamrta------2:19:167------purport).

One has to develop his devotional service under the directions of a pure devotee, the spiritual master, and in accordance with the Vedic directions given in the Pañcarātra and Bhāgavata systems. The Pañcarātra system includes methods of temple worship, and the Bhāgavata system includes the spreading of Kṛṣṇa conscious philosophythrough the recitation of Śrīmad-Bhāgavatam and the discussion of philosophy with people who are interested.
(Sri Caitanya Caritamrta------2:19:169------purport).