Bhagavad Geeta: Chapter 2, Verses 22-28
Our transcendental nature is pointed to in the previous verses by Sri Krishna, where he says that the Self is not any of the six changes that the body goes through, nor is it the mind with its ever-changing thoughts. The Self remains untouched and free of all modifications. Sri Krishna also indicates that a person who can endure the changes in body and mind level, with equipoise, is eligible to experience the immortal Self.
When we take ourselves as the BMI (body, mind, and intellect), we suffer because of the inevitable changes which happen to them. Suffering is not because of the presence of the BMI, but it is because of our identification with them. Throughout the day, we identify with the body and mind. That is why we suffer through all the changes happening to the body and mind.
Identifying with BMI, one becomes the doer. Every action has a result, and he becomes the enjoyer. When a person identifies with the true nature of Self, he is neither the doer nor the enjoyer. Self is nirvīkara (changeless), and it is advitiyāya (non-dual). It cannot kill, be killed, or cannot be the cause to kill.
Chapter 2, Verse 22
Just as a person casts off worn-out garments and wears new ones, likewise, the embodied Self casts off its worn-out body and enters a new one.
When a dress becomes old or when we need to work in a new field, we wear a dress suitable for that occasion or work. Similarly, when the body is no longer useful, the indweller (mind and intellect) takes up a new body to enter into an appropriate environment to fulfill the next desires/plans (a field suitable to exhaust the vāsanās). Just as one changes clothes, one changes body because the old body is no more useful. Evolution and change are needed for the body and mind, not the Self. The Self is perfect and changeless, it needs no evolution. Why is that? Sri Krishna continues to explain.
Chapter 2, Verses 23, 24 and 25
Weapons cannot shred the Self, nor can fire burn it. Water cannot moisten it, nor can the wind dry it.
This Self cannot be cut or burnt; it can neither be moistened nor dried up. It is eternal, all-pervading, stable, immovable, and ancient.
This Self is spoken of as unmanifest, unthinkable, and unchangeable. Knowing this, you should not grieve.
Weapons cannot shred the Self. A weapon can cut (destroy) an object but can’t cut water, fire, air, or space. The principle is that an element cannot destroy another element that is subtler than itself. Since the Self is subtler than space, weapons cannot shred it.
For eg, if one eats an apple in a dream, that doesn't satisfy the hunger of a man after he wakes up, because they are both in different realms. Similarly, the Self is in a different realm that is transcending time. Everything in the world changes. All these changes take place in the realm of time and these cannot touch the Self.
The unknown Self is being explained with reference to the known (objects). We can see the smoke and conclude that there is fire. Fire is comprehended. In the same way, we cannot see something and infer the presence of the Self with the senses. The Self is the subject, because of which we can perceive and conceive objects with the senses. In this way, Sri Krishna explains to Arjuna that what is dying (changing) is only the names and forms, Atman is eternal, and that he should not be overwhelmed by these misplaced emotions that are obstructing him from doing his duty.
Chapter 2, Verses 26 and 27
Even if you think that the Self is subject to constant birth and death, O mighty-armed (Arjuna), even then you should not grieve like this.
Death is certain for one who has been born, and birth is certain for one who has died. Therefore, you should not grieve over the inevitable.
From verses 2.11 to 2.25, Sri Krishna lectured from the perspective of the highest standpoint. Sri Krishna understands that probably Arjuna didn’t get it, so he comes down one notch. He says that even if Arjuna sees Self as going through constant birth and constant death, then also there is no need to worry. It is unavoidable that which is born must die. And that which dies will be born again. There is no remedy for it. Why worry about it then.
Chapter 2, Verse 28
O scion of Bharat, all created beings are unmanifest before birth, manifest in life, and again unmanifest on death. So why grieve?
We were unmanifest a hundred years ago, which means no one was able to perceive us at that time. Then we manifested temporarily to experience life. And with death, we unmanifest again to go back to where we came from. So there is no need to grieve.