This verse more clearly explains the real nature of the soul, which is spread all over the body. Anyone can understand what is spread all over the body: it is consciousness. Everyone is conscious of the pains and pleasures of the body in part or as a whole. This spreading of consciousness is limited within one's own body. The pains and pleasures of one body are unknown to another. Therefore, each and every body is the embodiment of an individual soul, and the symptom of the soul's presence is perceived as individual consciousness. This soul is described as one ten-thousandth part of the upper portion of the hair point in size. The Svetasvatara Upanisad confirms this:
balagra-sata-bhagasya satadha kalpitasya ca
bhago jivah sa vijneyah sa canantyaya kalpate.
"When the upper point of a hair is divided into one hundred parts and again each of such parts is further divided into one hundred parts, each such part is the measurement of the dimension of the spirit soul." (Svet. 5.9) Similarly, in the Bhagavatam the same version is stated:
kesagra-sata-bhagasya satamsah sadrsatmakah
jivah suksma-svarupo 'yam sankhyatito hi cit-kanah
"There are innumerable particles of spiritual atoms, which are measured as one ten-thousandth of the upper portion of the hair."
Therefore, the individual particle of spirit soul is a spiritual atom smaller than the material atoms, and such atoms are innumerable. This very small spiritual spark is the basic principle of the material body, and the influence of such a spiritual spark is spread all over the body as the influence of the active principle of some medicine spreads throughout the body. This current of the spirit soul is felt all over the body as consciousness, and that is the proof of the presence of the soul. Any layman can understand that the material body minus consciousness is a dead body, and this consciousness cannot be revived in the body by any means of material administration. Therefore, consciousness is not due to any amount of material combination, but to the spirit soul. In the Mundaka Upanisad the measurement of the atomic spirit soul is further explained:
eso 'nuratma cetasa veditavyo
yasmin pranah pancadha samvivesa
pranais cittam sarvam otam prajanam
yasmin visuddhe vibhavaty esa atma.
"The soul is atomic in size and can be perceived by perfect intelligence. This atomic soul is floating in the five kinds of air [prana, apana, vyana, samana and udana], is situated within the heart, and spreads its influence all over the body of the embodied living entities. When the soul is purified from the contamination of the five kinds of material air, its spiritual influence is exhibited." (Mund. 3.1.9)
The hatha-yoga system is meant for controlling the five kinds of air encircling the pure soul by different kinds of sitting postures—not for any material profit, but for liberation of the minute soul from the entanglement of the material atmosphere.
So the constitution of the atomic soul is admitted in all Vedic literatures, and it is also actually felt in the practical experience of any sane man. Only the insane man can think of this atomic soul as all-pervading Visnu-tattva.
The influence of the atomic soul can be spread all over a particular body. According to the Mundaka Upanisad, this atomic soul is situated in the heart of every living entity, and because the measurement of the atomic soul is beyond the power of appreciation of the material scientists, some of them assert foolishly that there is no soul. The individual atomic soul is definitely there in the heart along with the Supersoul, and thus all the energies of bodily movement are emanating from this part of the body. The corpuscles which carry the oxygen from the lungs gather energy from the soul. When the soul passes away from this position, activity of the blood, generating fusion, ceases. Medical science accepts the importance of the red corpuscles, but it cannot ascertain that the source of the energy is the soul. Medical science, however, does admit that the heart is the seat of all energies of the body.
Such atomic particles of the spirit whole are compared to the sunshine molecules. In the sunshine there are innumerable radiant molecules. Similarly, the fragmental parts of the Supreme Lord are atomic sparks of the rays of the Supreme Lord, called by the name prabha or superior energy. Neither Vedic knowledge nor modern science denies the existence of the spirit soul in the body, and the science of the soul is explicitly described in the Bhagavad-gita by the Personality of Godhead Himself.
The material body is perishable by nature. It may perish immediately, or it may do so after a hundred years. It is a question of time only. There is no chance of maintaining it indefinitely. But the spirit soul is so minute that it cannot even be seen by an enemy, to say nothing of being killed. As mentioned in the previous verse, it is so small that no one can have any idea how to measure its dimension. So from both viewpoints there is no cause of lamentation because the living entity can neither be killed as he is, nor can the material body, which cannot be saved for any length of time, be permanently protected. The minute particle of the whole spirit acquires this material body according to his work, and therefore observance of religious principles should be utilized. In the Vedanta-sutras the living entity is qualified as light because he is part and parcel of the supreme light. As sunlight maintains the entire universe, so the light of the soul maintains this material body. As soon as the spirit soul is out of this material body, the body begins to decompose; therefore it is the spirit soul which maintains this body. The body itself is unimportant. Arjuna was advised to fight and sacrifice the material body for the cause of religion.
When an embodied living entity is hurt by fatal weapons, it is to be known that the living entity within the body is not killed. The spirit soul is so small that it is impossible to kill him by any material weapon, as is evident from the previous verses. Nor is the living entity killable because of his spiritual constitution. What is killed, or is supposed to be killed, is the body only. This, however, does not at all encourage killing of the body. The Vedic injunction is, " mahimsyat sarva-bhutani " never commit violence to anyone. Nor does understanding that the living entity is not killed encourage animal slaughter. Killing the body of anyone without authority is abominable and is punishable by the law of the state as well as by the law of the Lord. Arjuna, however, is being engaged in killing for the principle of religion, and not whimsically.
Qualitatively, the small atomic fragmental part of the Supreme Spirit is one with the Supreme. He undergoes no changes like the body. Sometimes the soul is called the steady, or kutastha. The body is subject to six kinds of transformations. It takes its birth in the womb of the mother's body, remains for some time, grows, produces some effects, gradually dwindles, and at last vanishes into oblivion. The soul, however, does not go through such changes. The soul is not born, but, because he takes on a material body, the body takes its birth. The soul does not take birth there, and the soul does not die. Anything which has birth also has death. And because the soul has no birth, he therefore has no past, present or future. He is eternal, ever-existing, and primeval—that is, there is no trace in history of his coming into being. Under the impression of the body, we seek the history of birth, etc., of the soul. The soul does not at any time become old, as the body does. The so-called old man, therefore, feels himself to be in the same spirit as in his childhood or youth. The changes of the body do not affect the soul. The soul does not deteriorate like a tree, nor anything material. The soul has no by-product either. The by-products of the body, namely children, are also different individual souls; and, owing to the body, they appear as children of a particular man. The body develops because of the soul's presence, but the soul has neither offshoots nor change. Therefore, the soul is free from the six changes of the body.
In the Katha Upanisad also we find a similar passage which reads:
na jayate mriyate va vipascin
nayam kutascin na vibhuva kascit
ajo nityah sasvato 'yam purano
na hanyate hanyamane sarire.
(Katha 1.2.18)
The meaning and purport of this verse is the same as in the Bhagavad-gita, but here in this verse there is one special word, vipascit, which means learned or with knowledge.
The soul is full of knowledge, or full always with consciousness. Therefore, consciousness is the symptom of the soul. Even if one does not find the soul within the heart, where he is situated, one can still understand the presence of the soul simply by the presence of consciousness. Sometimes we do not find the sun in the sky owing to clouds, or for some other reason, but the light of the sun is always there, and we are convinced that it is therefore daytime. As soon as there is a little light in the sky early in the morning, we can understand that the sun is in the sky. Similarly, since there is some consciousness in all bodies—whether man or animal—we can understand the presence of the soul. This consciousness of the soul is, however, different from the consciousness of the Supreme because the supreme consciousness is all-knowledge—past, present and future. The consciousness of the individual soul is prone to be forgetful. When he is forgetful of his real nature, he obtains education and enlightenment from the superior lessons of Krsna. But Krsna is not like the forgetful soul. If so, Krsna's teachings of Bhagavad-gita would be useless.
There are two kinds of souls—namely the minute particle soul (anu-atma) and the Supersoul (the vibhu-atma). This is also confirmed in the Katha Upanisad in this way:
anor aniyan mahato mahiyan
atmasya jantor nihito guhayam
tam akratuh pasyati vita-soko
dhatuh prasadan mahimanam atmanah
(Katha 1.2.20)
"Both the Supersoul [Paramatma] and the atomic soul [jivatma] are situated on the same tree of the body within the same heart of the living being, and only one who has become free from all material desires as well as lamentations can, by the grace of the Supreme, understand the glories of the soul." Krsna is the fountainhead of the Supersoul also, as it will be disclosed in the following chapters, and Arjuna is the atomic soul, forgetful of his real nature; therefore he requires to be enlightened by Krsna, or by His bona fide representative (the spiritual master).
Everything has its proper utility, and a man who is situated in complete knowledge knows how and where to apply a thing for its proper utility. Similarly, violence also has its utility, and how to apply violence rests with the person in knowledge. Although the justice of the peace awards capital punishment to a person condemned for murder, the justice of the peace cannot be blamed because he orders violence to another person according to the codes of justice. In Manu-samhita, the lawbook for mankind, it is supported that a murderer should be condemned to death so that in his next life he will not have to suffer for the great sin he has committed. Therefore, the king's punishment of hanging a murderer is actually beneficial. Similarly, when Krsna orders fighting, it must be concluded that violence is for supreme justice, and, as such, Arjuna should follow the instruction, knowing well that such violence, committed in the act of fighting for Krsna, is not violence at all because, at any rate, the man, or rather the soul, cannot be killed; so for the administration of justice, so-called violence is permitted. A surgical operation is not meant to kill the patient, but to cure him. Therefore the fighting to be executed by Arjuna at the instruction of Krsna is with full knowledge, so there is no possibility of sinful reaction.