SB 1.3.21
tatah saptadase jatah
satyavatyam parasarat
cakre veda-taroh sakha
drstva pumso ’lpa-medhasah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Thereafter, in the seventeenth incarnation of Godhead, Sri Vyasadeva appeared in the womb of Satyavati through Parasara Muni, and he divided the one Veda into several branches and subbranches, seeing that the people in general were less intelligent.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Originally the Veda is one. But Srila Vyasadeva divided the original Veda into four, namely Sama, Yajur, Rg, 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-bandhus, 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 into various branches and subbranches for the sake of the less intelligent classes like the dvija-bandhus, sudras and women.