Narottama dāsa Ṭhākura has said that if you want to make concrete progress in spiritual life, then you have to corroborate the statement of the scriptures, the statements of saintly person, and statements of the spiritual master-three things. Why three things? Because a spiritual master means he does not place anything which is not in the scriptures. He does not say that "My theory is like this." That is not a spiritual master. Similarly sādhu, saintly person, also does not say anything which is not mentioned in the scriptures. He does not manufacture anything by mental concoction. And what is śāstra, scriptures?
They are statement of different saintly persons and spiritual masters. Therefore one has to corroborate these three things: scriptures, and statement of saintly persons, and statement of spiritual master. The spiritual master is via media. The disciple, if he cannot understand the statement of the scriptures or any saintly person, he submits his doubts before the spiritual master and he clears it. In this way we have to make progress. So Prahlāda Mahārāja says that a person, even if he is a brāhmaṇa with good qualification, if he is not a devotee of the Lord, then he is good for nothing. He says, "He is good for nothing." Viprād dvi-ṣad-guṇa-yutāt. And when who is good? Now, śvapacaṁ variṣṭham. Better than him, even a person is born of a very low family... In India it is considered according to Vedic, that low family is considered one who eats the dog, dog-eaters.
Of course, there are many kinds of flesh-eaters, but when a man becomes the eater of dog flesh, he is considered to be very low. So śvapacaṁ variṣṭham. So there is a class in India, they are called caṇḍāla. Everywhere there is. They eat dog flesh. So Prahlāda Mahārāja says, "It doesn't matter. But if he is a devotee of Lord, he is better than that brāhmaṇa, that brāhmaṇa with good qualifications. And he, although he is born of a low family..." Śvapacaṁ variṣṭham. Why he is variṣṭham? Now, manye tad-arpita-mano: "Because his mind and attention is always engaged in the service of the Lord." That is his qualification. That is making him purified in every moment. Śṛṇvatāṁ sva-kathāḥ-kṛṣṇaḥ puṇya-śravaṇa-kīrtanaḥ [SB 1.2.17].
Prabhupada's lecture - Śrīmad-Bhāgavatam 7.9.10 Montreal, July 9, 1968