Kṛṣṇa is explaining the subject matter of knowledge. First of all Kṛṣṇa has explained the process of knowledge. Amānitvam adambhitvaṁ kṣāntir ārjavam (BG 13.8).
Mayi cānanya-yogena bhaktir avyabhicāriṇī (BG 13.11). Janma-mṛtyu-jarā-vyādhi-duḥkha-doṣānudarśanam (BG 13.9). These are the process of knowledge, to know. If we remain befooled, ignorant, that we are missing the chance.
Everything we can know. This human form of body is specially meant for that purpose. You can understand what you are, what is this material nature, what is God and how we are related, how things are going on. Everything is there, but we are so foolish that we do not take care. We live like cats and dogs, eat something and sleep and have sexual intercourse, and then we are afraid always and then die. This is cats' and dogs' life. Real life is to know, athāto brahma jijñāsā. That is real life, human life. One must be inquisitive to understand the Absolute Truth, brahma-jijñāsā, not inquiring in the market, "What is the rate of share?" "What is the rate of rice?" No, not for this inquiry. Jijñāsuḥ śreya uttamam: to inquire about the Absolute Truth, uttamam, beyond this material nature. Udgata tamam. This material nature is called tama. Tamaso mā jyotir gama. These are the Vedic injunction.
You have to enter, you have to understand the world of light. This world is the world of darkness. It is simply . . . we require, therefore, sunlight, moonlight, electric light. Otherwise it is dark. It is called tamaḥ. But there is another world, which is full of light. It is so full of light that you do not require the sunlight, moonlight or electric light there.