Śrīmad-Bhāgavatam 7.9.10
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Montreal, July 10, 1968
So to come to this platform of confidence or Kṛṣṇa consciousness, there is training. That training is called viddhi-mārga, regulative principles, following the regulative principles. So this whole varṇāśrama system, Vedic system, the different caste—brāhmaṇa, kṣatriya, vaiśya, śūdra, a brahmacārī, gṛhastha, vānaprastha, sannyāsa—they are very scientifically designed to elevate one gradually to the standard of "no fear," "fearfulnessless," no more fear, confident. So vipra means just the previous stage of becoming completely a brāhmaṇa. Janmanā jāyate śūdraḥ: "By birth everyone is born a śūdra." Saṁskārād bhaved dvijaḥ: "When he goes to the spiritual master and the spiritual master initiates him, at that time his second birth is there, dvija." Dvija. The birds are called also dvija because they get twice birth. Once they come as egg, the form of birth in the egg, and then, when they come out from the egg and the shell, break the shell and come out, that is real life. Similarly, we are in the egg, within the shell of ignorance. So when we come out from the shell of ignorance, that is our second birth.
The first birth is by father and mother, and the second birth is by the spiritual master and Vedic knowledge. There is also mother. The Vedic knowledge is mother, and the spiritual master is the father. So saṁskārād bhaved dvijaḥ. The spiritual master trains the student gradually. That is called initiation. That is called dvija. Janmana jāyate śūdraḥ: "By birth by the father and mother, everyone is śūdra." It doesn't matter where he takes his birth, not that only India they are brāhmaṇa, kṣatriya, vaiśya, śūdra. Everywhere. Cātur-varṇyam mayā sṛṣṭaṁ guṇa-karma-vibhāgaśaḥ [Bg. 4.13]. In the Bhagavad-gītā you'll find that these four system of social division—brāhmaṇa, kṣatriya, vaiśya, śūdra—they are all over the universe, not that... Don't think that it is in India. Everywhere.