When one is accepted as a brāhmaṇa in the sacred thread ceremony under the pāñcarātrika system, then he is dvija, twice-born. That is confirmed by Sanātana Gosvāmī: dvijatvaṁ jāyate. By the process of initiation by the spiritual master, a person is accepted as a brāhmaṇa in his purified state of chanting the holy name of the Lord. He then makes further progress to become a qualified Vaiṣṇava, which means that the brahminical qualification is already acquired.
(Srimad Bhagavatam-----3:33:6-----purport).

It is said that once a poor brāhmaṇa worshiped Lord Śiva for a benediction, and Lord Śiva advised the devotee to go to see Sanātana Gosvāmī. The devotee went to Sanātana Gosvāmī and informed him that Lord Śiva had advised him to seek out the best benediction from him (Sanātana). Sanātana had a touchstone with him, which he kept with the garbage. On the request of the poor brāhmaṇa, Sanātana Gosvāmī gave him the touchstone, and the brāhmaṇa was very happy to have it. He now could get as much gold as he desired simply by touching the touchstone to iron. But after he left Sanātana, he thought, "If a touchstone is the best benediction, why has Sanātana Gosvāmī kept it with the garbage?" He therefore returned and asked Sanātana Gosvāmī, "Sir, if this is the best benediction, why did you keep it with the garbage?" Sanātana Gosvāmī then informed him, "Actually, this is not the best benediction. But are you prepared to take the best benediction from me?" The brāhmaṇa said, "Yes, sir. Lord Śiva has sent me to you for the best benediction." Then Sanātana Gosvāmī asked him to throw the touchstone in the water nearby and then come back. The poor brāhmaṇa did so, and when he returned, Sanātana Gosvāmī initiated him with the Hare Kṛṣṇa mantra. Thus by the benediction of Lord Śiva the brāhmaṇa got the association of the best devotee of Lord Kṛṣṇa and was thus initiated in the mahā-mantra, Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare.
(Srimad Bhagavatam-----4:7:6-----purport).

There is no bar to propagating the Kṛṣṇa consciousness movement even among people who are born in caṇḍāla, mleccha or yavana families. Even in India, this point has been enunciated by Śrīla Sanātana Gosvāmī in his book Hari-bhakti-vilāsa, which is smṛti and is the authorized Vedic guide for Vaiṣṇavas in their daily behavior. Sanātana Gosvāmī says that as bell metal can turn to gold when mixed with mercury in a chemical process, so, by the bona fide dīkṣā, or initiation method, anyone can become a Vaiṣṇava.
(Srimad Bhagavatam-----4:8:54-----purport).

When Sanātana Gosvāmī went to see Lord Śrī Caitanya Mahāprabhu, he could not be recognized by Candraśekhara Ācārya. The conclusion is that the Supreme Personality of Godhead is situated in everyone's heart, and His pure devotees, the Vaiṣṇavas, are also traveling all over the world, but those who are under the modes of material nature cannot understand the form of the Supreme Personality of Godhead, the source of this cosmic manifestation, or the Vaiṣṇavas. It is said, therefore, that one cannot see the Supreme Personality of Godhead or a Vaiṣṇava with these material eyes.
(Srimad Bhagavatam-----4:22:9-----purport).

The real vidvān is one who tries to understand his own position within this material world. For example, when Sanātana Gosvāmī submitted to the lotus feet of Śrī Caitanya Mahāprabhu, his first question was 'ke āmi', 'kene āmāya jāre tāpa-traya'. In other words, he wanted to know his constitutional position and why he was suffering from the threefold miseries of material existence. This is the process of education.
(Srimad Bhagavatam-----7:6:16-----purport).

In Caitanya-caritāmṛta, in connection with Lord Caitanya's instructions to Sanātana Gosvāmī, it is explained that a devotee should externally execute his routine devotional service in a regular way but should always inwardly think of the particular mellow in which he is attracted to the service of the Lord. This constant thought of the Lord makes the devotee eligible to return home, back to Godhead.
(Srimad Bhagavatam-----7:10:40-----purport).

As stated in Bhagavad-gītā (15.15) by the Supreme Personality of Godhead, Kṛṣṇa, the purpose of studying the Vedas is to understand Him (vedaiś ca sarvair aham eva vedyaḥ). Śrī Caitanya Mahāprabhu explained to Sanātana Gosvāmī that there are three purposes in the Vedas. One is to understand our relationship with Kṛṣṇa (sambandha), another is to act according to that relationship (abhidheya), and the third is to reach the ultimate goal (prayojana).
(Srimad Bhagavatam-----10:8:45-----purport).

Śrīla Viśvanātha Cakravartī Ṭhākura, quoting from the Vaiṣṇava-toṣaṇī of Śrīla Sanātana Gosvāmī, says that the incident of Kṛṣṇa's breaking the pot of yogurt and being bound by mother Yaśodā took place on the Dīpāvalī Day, or Dīpa-mālikā. Even today in India, this festival is generally celebrated very gorgeously in the month of Kārtika by fireworks and lights, especially in Bombay. It is to be understood that among all the cows of Nanda Mahārāja, several of mother Yaśodā's cows ate only grasses so flavorful that the grasses would automatically flavor the milk.
(Srimad Bhagavatam-----10:9:1-2-----purport).

Śrīla Sanātana Gosvāmī is the ideal spiritual master, for he delivers one the shelter of the lotus feet of Madana-mohana. Even though one may be unable to travel on the field of Vṛndāvana due to forgetfulness of his relationship with the Supreme Personality of Godhead, he can get an adequate opportunity to stay in Vṛndāvana and derive all spiritual benefits by the mercy of Sanātana Gosvāmī. Śrī Govindajī acts exactly like the śikṣā-guru (instructing spiritual master) by teaching Arjuna the Bhagavad-gītā. He is the original preceptor, for He gives us instructions and an opportunity to serve Him. The initiating spiritual master is a personal manifestation of Śrīla Madana-mohana vigraha, whereas the instructing spiritual master is a personal representative of Śrīla Govindadeva vigraha. Both of these Deities are worshiped at Vṛndāvana. Śrīla Gopīnātha is the ultimate attraction in spiritual realization.
(Sri Caitanya Caritamrta-----1:1:47-----purport).

From the teachings of Lord Caitanya Mahāprabhu to Sanātana Gosvāmī (CC-2:22:65) we learn:
śāstra-yuktye sunipuṇa, dṛḍha-śraddhā yāṅra
"uttama-adhikārī" sei tāraye saṁsāra
"A person who is expert in understanding the conclusion of the revealed scriptures and who fully surrenders to the cause of the Lord is actually able to deliver others from the clutches of material existence." Śrīla Rūpa Gosvāmī, in his Upadeśāmṛta (3), advises that to make rapid advancement in the cult of devotional service one should be very active and should persevere in executing the duties specified in the revealed scriptures and confirmed by the spiritual master. Accepting the path of liberated souls and the association of pure devotees enriches such activities.
(Sri Caitanya Caritamrta-----1:2:117-----purport).