Krishna is making the case that the self (atman) is fundamentally indestructible. Having said in 2.22 that the self simply changes bodies like changing clothes, he now goes further: no physical force, no element of the natural world, can actually touch it.
nainaṃ chindanti śastrāṇi nainaṃ dahati pāvakaḥ | na cainaṃ kledayanty āpo na śoṣayati mārutaḥ ||
Weapons do not cut this (the self); fire does not burn it; water does not wet it; wind does not dry it.
Arjuna's breakdown in Chapter 1 was rooted in the belief that fighting would cause irreversible loss: Bhishma gone, Drona gone, kin gone. Krishna is dismantling the premise. The people Arjuna is grieving for cannot actually be destroyed in the way he imagines. The body changes; the self does not.
Ancient Indian thought held that all physical reality was composed of four or five elements. By saying that none of these can affect the self, Krishna is not just listing examples. He is saying: every mechanism of physical change you can name leaves the self untouched. This is a logical closure, not a poetic flourish.
Fear of death is fear that something will be permanently lost or destroyed. Krishna is pointing out that the thing you think is at risk is not actually reachable. You cannot fear the destruction of something that is, by its nature, indestructible. The fear is built on a category error: treating the self as if it were body-stuff.
Krishna is not trying to make Arjuna feel better by minimizing the loss. He is trying to redefine what 'loss' actually means. If the self is indestructible, then death is not destruction. It is a change of form. Arjuna's grief is real; the premise behind it is not accurate.
Person A is a founder who has tied their entire identity to the company they built. When it fails, or when they are pushed out, it feels like annihilation: like the thing that made them 'them' has been cut away. They spiral. They cannot act. The failure burns them. Person B has also built something, also lost it. But they have, through some mix of experience and reflection, separated what they ARE from what they BUILT. The loss is real. It hurts. But something in them watches the grief without becoming the grief. They pick up, start again, not because they are numb but because they can feel the difference between a wound to the body-self and a wound to whatever is underneath.
Verse 2.24 continues the same argument, piling on more descriptors of the self: unbreakable, incombustible, pervasive, stable. It is Krishna building a complete portrait of what the indestructible self actually is. When ready, say: "2.24"