SB 1.3.21

Originally the Veda is one. But Śrīla Vyāsadeva divided the original Veda into four, namely Sāma, Yajur, Ṛg, Atharva, and then again they were explained in different branches like the Purāṇas and the Mahābhārata. Vedic language and the subject matter are very difficult for ordinary men. They are understood by the highly intelligent and self-realized brāhmaṇas. But the present Age of Kali is full of ignorant men. Even those who are born by a brāhmaṇa father are, in the present age, no better than the śūdras or the women. The twice-born men, namely the brāhmaṇas, kṣatriyas and vaiśyas, are expected to undergo a cultural purificatory process known as saṁskāras, but because of the bad influence of the present age the so-called members of the brāhmaṇa and other high-order families are no longer highly cultured. They are called the dvija-bandhus, or the friends and family members of the twice-born. But these dvija-bandhus are classified amongst the śūdras and the women. Śrīla Vyāsadeva divided the Vedas into various branches and subbranches for the sake of the less intelligent classes like the dvija-bandhus, śūdras and women.