SB 1.4.25
stri-sudra-dvijabandhunam
trayi na sruti-gocara
karma-sreyasi mudhanam
sreya evam bhaved iha
iti bharatam akhyanam
krpaya munina krtam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Out of compassion, the great sage thought it wise that this would enable men to achieve the ultimate goal of life. Thus he compiled the great historical narration called the Mahabharata for women, laborers and friends of the twice-born.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The friends of the twice-born families are those who are born in the families of brahmanas, ksatriyas and vaisyas, or the spiritually cultured families, but who themselves are not equal to their forefathers. Such descendants are not recognized as such, for want of purificatory achievements. The purificatory activities begin even before the birth of a child, and the seed-giving reformatory process is called garbhadhana-samskara. One who has not undergone such garbhadhana-samskara, or spiritual family planning, is not accepted as being of an actual twice-born family. The garbhadhana-samskara is followed by other purificatory processes, out of which the sacred thread ceremony is one. This is performed at the time of spiritual initiation. After this particular samskara, one is rightly called twice-born. One birth is calculated during the seed-giving samskara, and the second birth is calculated at the time of spiritual initiation. One who has been able to undergo such important samskaras can be called a bona fide twice-born.
If the father and the mother do not undertake the process of spiritual family planning and simply beget children out of passion only, their children are called dvija-bandhus. These dvija-bandhus are certainly not as intelligent as the children of the regular twice-born families. The dvija-bandhus are classified with the sudras and the woman class, who are by nature less intelligent. The sudras and the woman class do not have to undergo any samskara save and except the ceremony of marriage.
The less intelligent classes of men, namely women, sudras and unqualified sons of the higher castes, are devoid of necessary qualifications to understand the purpose of the transcendental Vedas. For them the Mahabharata was prepared. The purpose of the Mahabharata is to administer the purpose of the Vedas, and therefore within this Mahabharata the summary Veda of Bhagavad-gita is placed. The less intelligent are more interested in stories than in philosophy, and therefore the philosophy of the Vedas in the form of the Bhagavad-gita, is spoken by the Lord Sri Krsna. Vyasadeva and Lord Krsna are both on the transcendental plane, and therefore they collaborated in doing good to the fallen souls of this age. The Bhagavad-gita is the essence of all Vedic knowledge. It is the first book of spiritual values, as the Upanisads are. The Vedanta philosophy is the subject matter for study by the spiritual graduates. Only the postgraduate spiritual student can enter into the spiritual or devotional service of the Lord. It is a great science, and the great professor is the Lord Himself in the form of Lord Sri Caitanya Mahaprabhu. And persons who are empowered by Him can initiate others in the transcendental loving service of the Lord.