People do not understand what is immortality. They think that it is a vague idea, because no knowledge. So many things . . . we are very proud of our advancement of knowledge. So many things we do not know, and it is not possible to know, even by our modern experimental knowledge. It is not possible. Therefore, if you want real knowledge, then you go to knowledge. Vedas mean knowledge. These Vedas means knowledge. Vetti veda vido jñāne. Veda, Veda means knowledge.
So if you want real knowledge, then you have to take shelter of these Vedas, Vedic literature, just like Īśopaniṣad. There are 108 Upaniṣads, out of which nine are very important. Out of that nine, this Īśopaniṣad stands first; then Taittirīya Upaniṣad, Māṇḍūkya Upaniṣad, Muṇḍaka Upaniṣad. So the Upaniṣad . . . upa, upa means nearing. So this knowledge will take you nearer to Kṛṣṇa.
And amongst the learned society, ācāryas, the śruti-pramāṇa . . . evidence is śruti. Śruti means these Vedas. They are not experimental knowledge. They are not knowledge established by the research work of contaminated, conditioned soul. Contaminated, conditioned soul, their senses are imperfect. They cannot see things as they are. Simply they theorize: "It may be like that." So much they can say. So "It may be like that," that is not knowledge. Knowledge, definite. There is no mistake.