SB 1.4 - The division of the Vedas
The four Vedas were entrusted to different sages for development in various ways: Ṛg Veda to Paila Ṛṣi, Sāma Veda to Jaimini, Yajur Veda to Vaiśampāyana, and the Atharva Veda to Aṅgirā. The Purāṇas and Itihāsās were entrusted to Romaharṣaṇa, the father of Sūta. All these learned sages, in turn, rendered their entrusted Vedas unto their many disciples, grand disciples and great grand disciples, and thus the respective branches of the followers of the Vedas came into being. The Vedic knowledge, broken into different branches by different disciplic succession, has been distributed all over the world. There are no branches of knowledge, either mundane or transcendental, which do not belong to the original Vedas. Vyāsa’s followers divided the four Vedas into 1130 branches. The Ṛg Veda was divided into 21 branches. The Yajur Veda into 100 branches, the Sāma Veda into 1000 branches, and Atharva Veda into 9 branches. Each of these branches has four subdivisions called Saṁhitā, Brāhmaṇa, Ārāṇyaka, and Upaniṣad. All together the four Vedas consist of 1130 Saṁhitās, 1130 Brāhmaṇas, 1130 Ārāṇyakas, and 1130 Upaniṣads - a total of 4520 titles.
Thus Vyāsa, who is very kind to the ignorant masses, edited the Vedas so they might be assimilated by less intellectual men. The Vedas cannot be easily understood by any ordinary person. There is a stricture that no one should learn the Vedas who is not a qualified brāhmaṇa. This stricture has been wrongly misinterpreted that the caste brāhmaṇas think that Vedas is their monopoly. Others take this as an injustice to members of other castes. But both of them are misguided. The Vedas had to be explained even to Brahmā, by the Supreme Lord. Thus the subject matter is understood only by those with exceptional qualities of goodness. Persons in the modes of passion and ignorance cannot understand the Vedas. The ultimate goal of Vedic knowledge is Śrī Kṛṣṇa, the Personality of Godhead, who cannot be understood by persons in passion and ignorance. Since in the present age, the mode of goodness is almost nil, Vyāsa divided the Vedas to help the less intelligent people in the lower modes.