SB 1.4 - Vyāsa's compassion for all classes
Out of great compassion, Vyāsa compiled the Mahābhārata for women, laborers and friends of the twice born, who were not qualified to hear the Vedas. There are different purificatory rites one need to undergo to be a proper twice born. The seed giving reformatory process if called garbhādhāna-saṁskāra. A second ceremony is done at the time of spiritual initiation when one is given the sacred thread. Thus one birth is calculated during the seed giving saṁskāra, and the second birth is calculated at the time of spiritual initiation. One who undergoes such reformatory rites can be called a bona fide twice born. The friends of the twice born are those who are born in the families of brāhmaṇas, kṣatriyas and vaiśyas but who have not undergone the purification process. These dvija-bandhus are classified with the śūdras and the women class, who do not have to undergo any saṁskāra except the marriage ceremony.
Since these classes do not have the necessary qualifications to understand the Vedas, Vyāsa prepared the Mahābhārata, which administers the purpose of the Vedas, and therefore within it, the summary Veda of Bhagavad-gītā is placed. The less intelligent are more interested in stories than philosophy, and therefore the philosophy of the Vedas in the form of Gītā is spoken by Lord Kṛṣṇa.