"Know that which pervades the entire body is indestructible. No one is able to destroy the imperishable soul." (Prabhupāda recites verse in Sanskrit)
Now it is very clearly enunciated, the nature of the soul. Any sensible man can understand. This is practical. Formerly, all the verses, they were more or less theoretical: dehino 'smin yathā dehe kaumāraṁ yauvanaṁ jarā (BG 2.13). This is, it may be taken theoretical. Not theoretically, but actually the fact, but still less intelligent cannot understand that there is a soul within this body. But here it is explained very clearly. Avināśi tu tad viddhi. Tat—that thing which is spread all over the body. Avināśi tu tad viddhi, tad—that, avināśi—imperishable. So what is spread all over the body? Consciousness. That is spread all over the body. Everyone can understand that if I pinch any part of my body or your any part of the body, you feel pain. Or similarly, if you get some other facilities, pleasure, so pains and pleasures are felt so long there is consciousness. Any man can understand. And as soon as the consciousness is not there, sometimes we are made unconsciousness by drugs, by chloroform and other anaesthetic medicine, or by nature, unconscious stage.
There are three stages: jāgarti, svapna, suṣupti. Anyone has got this experience. One stage is that you are awakened, another stage is sleeping, and another stage is unconscious. Jāgarti, svapna and suṣupti, the Sanskrit name. Jāgarti, when you are awakened, our consciousness is very acute, very strong. In sleeping stage, there is consciousness, but it is not so active. And unconscious stage means consciousness is some way or other subdued, not working. Three stages. So death means that unconsciousness for a long period. That is death. Because the soul is eternal. It will be explained. There is no birth and death. So when this body is annihilated, so the soul remains unconscious for a period, seven months for a human being. Seven months unconscious stage within the womb of the mother. After seven months, the consciousness revives.