Bhagavad Gita Verse 23-24, Chapter 2

nainam chindanti shastraani nainam dahati paavakaha |
na chainam kledayanyaapo na shooshayati maaritaha || 23 ||
 
acchedyoyamadaahyoyamakledyoshoshya eva cha |
nityaha sarvagataha sthaanurchaloyam sanaatanaha || 24 ||
 
Weapons cannot pierce this (the eternal essence), fire cannot burn this, water cannot wet this, and wind cannot dry this.
 
This is uncleavable, incombustible, and cannot be wetted or dried. It is eternal, all-pervading, stable, immovable and everlasting.
 
enam : this (eternal essence)
na chindanti : cannot pierce
shastraani : weapons
na dahati : cannot burn
paavakaha : fire
cha : and
na kledayanti : cannot wet
aapaha : water
na shoshayati : cannot dry
maarutaha : wind
 
acchedyaha : uncleavable
ayam : this (eternal essence)
adaahyoha : incombustible
akledyo : wetted
shoshya : dried
eva cha : neither can
nityaha : eternal
sarvagataha : all-pervading
sthaanuha : stable
achalaha : immovable
sanaatanaha : eternal
 
We have been hearing a lot about the eternal essence since the 13th shloka began. By now, it must be clear to us that the topic of the eternal essence is abstract, and our intellect will have difficulty in grasping it. This is perfectly normal, because the eternal essence cannot be fully comprehended by the intellect. But we can get close to it through negation.
 
What does negation mean? Let's say you want your friend to buy a shirt for you from the store. You will inform your friend about that the shirt is fuchsia color. If you were to use negation, you would say that the shirt is not regular pink, not dark pink, not fully bright pink etc.
 
Similarly, the eternal essence here is indicated by negation, that it cannot be cut, cannot be wetted or dried etc.
 
Shri Krishna will provide us with a few more shlokas about the eternal essence, after which the topic will change to something much more tangible and concrete.
 
Footnotes
1. The Jnyaneshwari, in the commentary for this shloka, declares that the eternal essence cannot be comprehended by our intellect.

Bhagavad Gita Verse 20, Chapter 2

na jaayate mriyate vaa kadaachinnaayam bhootvaa bhavitaa vaa na bhooyaha |
ajo nityaha shaashvatoyam puraano na hanyate hanyamaane shareere || 20 ||
 
It (the eternal essence) is neither born, nor does it ever die; nor is it that having come into existence, it will again cease to exist. It is birthless, eternal, changeless and primeval, it is not slain when the body is killed.
 
na : not
jaayate : born
mriyate : dies
vaa : and
kadaachita : ever
na : not
ayam : this
bhootvaa : having come into existence
abhavitaa : ceases to be
vaa na : it is not the case that
bhooyaha : again
ajaha : birthless
nityaha : timeless
shaashvataha : changeless
puraano : primeval
na hanyate : slain
hanyamaane : when slain
shareere : the body
 
This shloka reinforces the attributes of the eternal essence that we have seen so far, that it is eternal and changeless. Any material object, including the human body, goes through six types of modifications: birth, exist, change, grow, decay, and to perish. The eternal essence is beyond all these modifications, hence it is changeless.
 
Two additional qualities of the eternal essence are provided here. The first is that it is birthless. It is logical that it should be birthless, otherwise it could not be eternal and timeless. And since it is birthless, it would have always existed, therefore it is primeval.
 
Note the change in meter to highlight the importance of this shloka.
 
Footnotes
1. "Om namoji aadya" is the very first ovi or stanza of the Jnyaneshwari. Sant Jnyaneshwar invokes the primeval quality of the eternal essence by using the word "aadya" which means primeval.