Bhagwad Gita - Post 20

Sri Krishna explains the nature of SELF thus:

Verse 21

Vedaavinaashinam nityam

ya enam ajam avyayam;
Katham sa purushah paartha

kam ghaatayati hanti kam.

(He is not born, nor does he ever die; after having been, he again ceases not to be. Unborn, eternal, changeless and ancient, he is not killed when the body is killed.)

An enlightened person who knows the changelessness and the indestructibility of the Self cannot perform the function of slaying or cause another to slay. When we know the Self to be invulnerable, how can anyone slay it?  The words ‘how can he slay' refer to Arjuna and `cause another to slay’ refer to Krishna's own role.

Lord Krishna explains that the soul being eternal is not subject to the six modifications of material existence which are: Existence, birth, growth, disease, decay and death. 

The soul is never born and never dies at any time. How can this be? It is not that the soul did not exist before and will not exist in the future. 

The soul exists eternally but opting the experiences of the material existence accepts a physical body. What did not exist in the past but is manifested only in the present is called conceived and that which exists now but will cease to exist eventually is called dead. 

But the soul is not conceived as it eternally exists and it will never die because it is immortal. 

With the 2 words ajah meaning unborn and nityam meaning eternal, it is made clear that the 2 modifications of birth and death are not applicable to the soul. 

In order to also negate the idea of the soul possessing any modifications by even being, Lord Krishna explains that the soul is everlasting which means it is free from being or nonbeing. The modification of any growth of the soul is neutralized by the word Puranah meaning ancient, that it always existed as it is. 

One possessing a body grows by the increase of the bodily parts; but the soul being bodiless does not increase it is the same eternally. 

The remaining 2 modifications of disease and decay are inapplicable by inference in understanding that the soul being eternal without any need to increase remains as it is and is changeless. 

Hence the soul being bereft of any of the six modifications of the physical body can never be destroyed even when the physical body is destroyed.

The word va occurring twice is used in the sense of and as in and the immortal soul does not come into existence by birth. The immortal soul is already by nature itself eternal. 

So existence by conception is proven false due to the fact the eternal soul is birthless. That which is conceived attains existence after birth; but that which already eternally exists by its own nature cannot be conceived again. This is the purport of this verse.

Katha Upanishad describes SELF thus:

NA JĀYATĒ MRIYATĒ VĀ VIPAŚCINNĀYAṄ KUTAŚCINNA BABHŪVA KAŚCIT.

AJŌ NITYAḤ ŚĀŚVATŌ.YAṄ PURĀṆŌ NA HANYATĒ HANYAMĀNĒ ŚARĪRĒ 

The intelligent Self is neither born nor does It die. It did not originate from anything, nor did anything originate from It. It is birth less, eternal, un decaying, and ancient. It is not injured even when the body is killed.

Vipascit, the intelligent One (Self)-intelligent, because Its nature of consciousness is never lost; 

na jayate, is not born-It is not produced; 

na va mriyate nor does It die. An impermanent thing that has origination, is subject to many modifications. 

With a view to denying all the modifications in the Self, the first and last of these modifications, in the form of birth and death, are being first denied here in the text: 'He is neither born nor dies.

Moreover, ayam, this One-the Self; 

na kutascit, did not come from anything-did not originate from any other cause; and from the Self Itself 

na kascit babhuva, nothing originated-as something different from It. 

Therefore, ayam, this Self (is),

ajah, birthless; 

nityah, eternal; 

sasvatah, undecaying. 

That which is impermanent is subject to decay, but this one is everlasting; therefore, It is 

puranah, ancient-new indeed even in the past. A thing is said to be new now, which emerges into being through the development of its parts, as for instance, a pot etc. 

The Self, however, is opposed to them. It is ancient, i.e. devoid of growth. 

Since this is so, therefore, 

na hanyate, It is not killed-not injured; 

sarire hanyamane, when the body is killed-with weapons etc.-though It exists there, just like space.

Love.