So the body is changing. Dehino 'smin yathā dehe kaumāraṁ yauvanaṁ jarā (BG 2.13). Kaumāram means boyhood. Yauvanam means youthhood, and jarā means old age, aged body. So I can remember, I am an old man, I can remember, I had a boy's body, I had a young man's body. Now I have got this aged body. So although the boyhood body, the youthhood body are no longer existing, but I am existing. That's a fact. Everyone can understand. He has got past, present, and future. You are all young boys and girls present here. So you had your past body as boyhood, childhood. Similarly, you have got your future body. That is awaiting. I have got it, you are awaiting. So past, future, past, present, and future, relatively we can understand in any condition of life. Therefore the conclusion is that when this aged body as I have got now... I am seventy-seven years old. So when this body will be finished, I'll get another body. As I have got consecutively from boyhood to childhood, childhood, I have, from childhood to boyhood, boyhood to youthhood, aged body, so why not next body? This is simple truth, that the living entity, or the soul, is transmigrating from one body to another. This is the basic principle of spiritual understanding. The vital force of the body is the spirit soul. It is not a mechanical arrangement of matter. The modern so-called scientists, they think that the body is combination of matter and, at a certain stage, these combination of matter develop living symptoms. But that is not a fact. If it is a fact, then the scientists can manufacture with chemicals a living body. But a scientist even up to date is unable to manufacture even a body like an ant, and what to speak of other, bigger animals.
So we have to take this knowledge from authority. Here is Kṛṣṇa speaking. He's authority. We accept Kṛṣṇa: the Supreme Personality of Godhead. His knowledge is perfect. He knows past, present, and future. Therefore, He is teaching Arjuna, "My dear Arjuna, the spirit soul within this body is eternal." That's a fact. Just like I can understand, I was in the past, I am in present, so I must be in the future. These are three phases of time, past, present, and future. In another place, we read in this Bhagavad-gītā, na jāyate na mriyate vā kadācit. The living entity is never born; neither it dies. Na jāyate means he never takes birth. Na jāyate na mriyate, it never dies. Nityaṁ śāśvato 'yam, na hanyate hanyamāne śarīre (BG 2.20). It is eternal, śāśvata, existing forever. Na hanyate hanyamāne śarīre (BG 2.20). By annihilation of this body, the soul does not die. Because... This is also confirmed in the Upaniṣads, Vedas: nityo nityānāṁ cetanaś cetanānām eko bahūnāṁ vidadhāti kāmān. The God is also eternal, and we are also eternal. We are part and parcels of God. Just like gold and fragments of gold; both of them are gold. Although I am fragment, a particle of gold or the spirit, still, I am spirit. So we get this information that both God and we, living entities, we are eternal. Nityo nityānām, nitya means eternal.