50 Kṛṣṇa Consciousness: the Topmost Yoga System
we should not hear of the Supreme Lord from one who is not purified.
One may ask, “How can you taint the words of Kṛṣṇa, which are naturally transcendentally pure? What is the harm if we hear from the nondevotee?” This question may be raised. The example given here is that milk is very nice and nutritious, but as soon as it is touched by a serpent it becomes poison immediately. The serpent is very envious. He bites and puts to death immediately, unnecessarily, and therefore is considered the cruelest animal amongst the living entities. In the  śāstra  nonviolence is recommended, as in every scripture, but the serpent and the scorpion are allowed to be killed. You cannot say that milk is so nutritious, and we can drink—what is the harm if it is touched by serpents? No—the result will be death. One should not hear at least the  Bhagavad-gītā  and the  Śrīmad-Bhāgavatam  from those who are not devotees of the Lord, who have no realization of God and who are envious of Him. Their touch renders it poison. The words of the Lord are always sublime, but as soon as they are touched by the serpent of a nondevotee, one should be very careful about hearing.
In the  Bhāgavatam , it is indicated that as soon as Śukadeva touched it, it became delicious. This is the distinction. Basically it is the ripened fruit of Vedic knowledge, but at the same time it has been touched by Śukadeva Gosvāmin.
The Lord is the supreme object of  yoga  and the reservoir of all transcendental pleasure; He reveals Himself only to His devotees and by the mercy of His devotees all can relish His intimate association.