SB 1.3.21

Originally the Veda is one. But Srila Vyasadeva divided the original Veda into four, namely Sama, Yajus, Rk, Atharva, and then again they were explained in different branches like the Puranas and the Mahabharata. Vedic language and the subject matter are very difficult for ordinary men. They are understood by the highly intelligent and self-realized brahmanas. But the present age of Kali is full of ignorant men. Even those who are born by a brahmana father are, in the present age, no better than the sudras or the women. The twice-born men, namely the brahmanas, ksatriyas and vaisyas, are expected to undergo a cultural purificatory process known as samskaras, but because of the bad influence of the present age the so-called members of the brahmana and other high order families are no longer highly cultured. They are called the dvija-bandhu or the friends and family members of the twice-born. But these dvija-bandhus are classified amongst the sudras and the women. Srila Vyasadeva divided the Vedas in various branches and sub-branches for the sake of the less intelligent classes like the dvija-bandhus, sudras and the women.