Hayagrīva: There was a lot of conjecture at this time on where the soul is located, and he writes, "It is likewise necessary to know that although the soul is joined to the whole body, there is yet in there a certain part in which it exercises its functions more particularly than in all the others, and that it is usually believed that this part is the brain or possibly the heart."
Prabhupāda: The heart.
Hayagrīva: "The brain because it is within..., because it is with that the organ of sense are connected, and the heart because it is apparently in it that we experience the passions." We... He thought that the soul was in the pineal gland at the base of the brain, because we think with the brain, but that he wasn't certain. He thought, "Well, our passions are in the heart, so maybe it's in the heart."
Prabhupāda: No.
Hayagrīva: "Maybe it's in the brain."
Prabhupāda: Therefore we have to accept God's instruction. He definitely gives the information, īśvaraḥ sarva-bhūtānāṁ hṛd-deśe arjuna tiṣṭhati (BG 18.61). Īśvaraḥ means the controller. So the soul is the controller of this body. So He is within the heart; it is already there. Īśvaraḥ sarva-bhūtānāṁ hṛd-deśe arjuna tiṣṭhati (BG 18.61). There are two kinds of īśvaraḥ, controller. One is the ordinary controller, that means the individual living being, and the other is the supreme living being. We get from Vedic information both of them sitting together on this body tree. So both cases, the Supersoul and the individual soul, they are living within the heart. That is the right conclusion.
Hayagrīva: But at the same time the soul pervades the entire body.
Prabhupāda: Yes. That is also explained in the Bhagavad-gītā. Avināśi tu tad viddhi yena sarvam idaṁ tatam. That portion which is spread all over the body, that is immortal. So this is the illumination or the shining of the soul. That the sun is situated localized in a particular place, that we can see everyday, but his illumination is distributed all over the universe. Similarly, although the soul is situated within the heart, his illumination is spread all over the body. So that is consciousness. So as soon as the soul is out from the heart, which is known as heart failure, when he leaves the heart, then what is the use of this heart? It becomes a lump of matter. Immediately consciousness is absent from the whole body. So it is upon the leaving of the soul this body there is no more consciousness. This is reasoning. Why a second before there was consciousness and after there is no consciousness? If you chopped up the body there will be no protest, there will be no feeling of pain, that "What is that?" This is reasoning, that something is missing. That soul has gone out; therefore the consciousness in the body is absent. That soul is immortal; the consciousness is also immortal. Now the consciousness, by the influence of illusory energy, is engaged in so many material things—consciousness of society, consciousness of nationality, consciousness of this, that, so many. This Kṛṣṇa consciousness movement is educating movement, how the consciousness can be purified to remain only Kṛṣṇa conscious. Then his life is successful.