In the last two slokas we saw the eternal nature of soul and the perishable nature of the body. But we see the body decaying and so it may be unnecessary to give so many reasons to prove body is decayable. However, it is not so and there are reasons to make this much of effort to say. Firstly, atman is not perishable like Him, the Paramatma. This is affirmative comparison. In a negative comparison, the atman is not like the body, which perishes. So, to establish the superiority of atman, destructible body is compared. Just as we come across dos and don’ts in our daily life, two types of examples were needed to show the indestructible quality of atman and so comparison with body was necessary. Another benefit also was found that by telling Arjuna that the body is perishable, his notion that he is going to kill Bheeshma and Drona would be changed. Though, in the fight he may destroy the bodies of these people, those bodies are anyway going to perish. Just by Arjuna not fighting, those bodies are not going to be everlasting. There can be many more factors to destroy those bodies. Also, by describing the decaying nature of the body, the impression of some that nourishments and tonics can keep this body eternal, can be cleared. Also, only if the perishable nature of body is understood, many persons who are suffering will at least derive peace that the ailments, which cause sufferings, will end with the perishing of the body. Since this body is going to perish, why bother so much about it? Some people also will derive this type of feeling. We may not spend money and time on unnecessary makeup to decorate this body. Lastly, we should get a balanced view about the body and not to think the body and soul are one and the same. These are the reasons why Sri Krishna took pains to explain the nature of the body and the soul. Having told this, He moves to the next sloka where He says that a person who does not understand the nature of soul and body is a fool:
ya enam vetti hantaram
yas cainam manyate hatam
ubhau tau na vijanito
nayam hanti na hanyate
“The two types of people, who think there are objects to destroy this [soul] and who think that this [soul] is destroyable, have not understood the nature [of the soul]”
Hantaram means objects or entities, which can kill. The first line means knowing that there are objects, which can kill a soul. Hatam manyate means believing as having been destroyed or killed. So the second line states that also believing that the soul as having been killed. Na vijanito means not understood. So these two categories of people, one thinking there are objects to destroy atman and the other who believe that the atman is destroyed, have not understood. Because, in the fourth line, it is stated that the atman is neither killed nor there are any objects capable of destroying the atman. Here objects means another soul as well as things causing destruction such as sword, arrow or bullet, etc. Therefore, the 19th sloka clearly says that there is nothing which can annihilate atman nor the atman ever gets annihilated.
Here another doubt may arise. This appears to be in contrast with some Veda sentences. Veda says ‘na himsyat sarvan bhoothani’. Do not be brutal [cause himsa] to any living creatures. The same Sri Krishna, Who gave the shastras asking us not to harm other living creatures, here, is advocating Arjuna that one cannot kill a soul. There seems to be contradiction. We may think, perhaps the shastras only ask us not to kill the bodies of other creatures. When Veda says cow slaughter should be avoided, does it mean the body of the cow should not be hurt? This is also not correct. Because, when someone dies, the body is cremated by igniting fire to the body. None calls this as himsa or hurting. So the shastras instruct us not to harm a body which is living or when the soul is inside. Therefore, the implication is that one should not cause maranam [death]. Maranam means mruth prana thyagena. That is separation of atman from the body and the Vedas advise us not to do this separation. So, the correct interpretation of the shastras is that, we are not authorized to separate the soul from the body. In fact, these words are similar to the words used in Katavalli Upanishad.