As I explained the other day, aihistam yat punar janmejaya, yat tat punar janmajayaya.(?) The whole effort was how to conquer over birth and death. So modern people they do not understand that birth and death can be conquered. They can imagine it. Sometimes they say that "By scientific advancement, someday we shall become immortal." They also expect to become immortal. But, expect or not expect, here is the information from Bhagavad-gītā. Kṛṣṇa says; He's not speaking something nonsense or utopian. It is fact that we should be interested in the permanent, permanent life, not temporary life. This life, this material life is temporary. We may live for ten years or ten hours. There are living entities, they live for ten minutes and there are living entities who are living for ten millions or ten billions of years. Just like in the Brahmaloka, they live billions of years. So all these duration of life, different types of duration of life, are there within this material world, but still, it is not permanent. Even if you live for ten billions of years or you live for ten minutes or ten seconds, it is nonpermanent. That is being explained here. Nāsato vidyate bhāvaḥ. Asataḥ, or this material body, it has no endurance, it will not endure, it will not be permanently existing. Nābhāvo vidyate sataḥ: And the soul is permanent. He, it has no change; it will never be nonexistent. Kṛṣṇa is explaining. When Kṛṣṇa says, "My dear Arjuna, you, Me, and all these kings and soldiers assembled here, it is not that we did not exist in the past," so what is that? That means we are not this body. This body was not existing in the past in my past life, or duration of life. But as I am soul, I am existing now, I did exist in the past, and I will exist in the future. That is sat. Therefore, spirit has no such change.
Narottama dāsa Ṭhākura has sung, sat-saṅga chāḍi' kainu asate vilāsa te kāraṇa lagilā mora karma-bandha-phāṅsa.