SB 3.7.29

The four statuses and orders of human society-brahmanas, ksatriyas, vaisyas and sudras, as well as brahmacaris, grhasthas, vanaprasthas and sannyasis-are all the divisions of quality, education, culture and spiritual advancement attained by practicing control of the mind and the senses. All these divisions are based on the particular nature of each individual person, not on the principle of birth. Birth is not mentioned in this verse because birth is immaterial. Vidura is famous in history as born of a sudrani mother, yet he is more than a brahmana by qualification because he is seen here to be the disciple of a great sage, Maitreya Muni. Unless one achieves at least the brahminical qualifications one cannot understand the Vedic hymns. Mahabharata is also a division of the Vedas, but it is meant for women, sudras and dvija-bandhus, the worthless children of the higher section. The less intelligent section of society can avail themselves of the Vedic instructions simply by studying the Mahabharata.