Kṛṣṇa says that either on this planet or in other planets in the outer space, or anywhere, the three qualities or three modes of material nature is working—the modes of goodness, the modes of passion and the modes of ignorance. Everywhere you'll find these three classes of living entities. Not three classes, four classes—the first class, goodness; second class, passion; third class, mixed passion and ignorance; and fourth class, ignorance. And below the fourth class, all fifth class, pañcama.
So according to these three modes of material nature, there must be division of the society. The first-class men are called brāhmaṇa, most learned scholar. Learned scholar means, as I was explaining, one who has complete knowledge of God. That is learned scholar. Otherwise, to know how to eat, how to sleep, how to have sexual intercourse and how to defend, this, these knowledge is also there in the animals. They know how to eat. There is no need of university for teaching how to eat or how to sleep or how to have sex life or how to defend. These are animal necessities. But actually human being should be still more advanced in knowledge. That knowledge is not comprising only eating, sleeping, mating and defending. That knowledge is to understand the Absolute Truth, God. That knowledge.
Therefore the Vedānta-sūtra philosophy, that begins with the word athāto brahma jijñāsā. Now, this life, this human form of life, is meant for inquiring about the Absolute Truth. Athāto brahma jijñāsā. Brahma means the Absolute Truth. So that should be the subject matter for studying in human form of life. So Bhagavad-gītā is the right book to understand about that Brahman, or the Supreme Personality of Godhead, or the Absolute Truth, whatever you call. The Absolute Truth is known in three phases: Brahman, Paramātmā and Bhagavān.