19. This verse is taken from the Kathopanisad Chapter I, Section ii, Mantra 19. This was also a favourite of R. W. Emerson who put the idea in a poem.
Atman neither acts nor is affected by the action. Krsna uses the word slayer and slain in the context of Arjuna’s dilemma. Atman is like fuel in your car. The fuel has no desire to go anywhere, is not responsible for the performance of the car or the quality of driving. It merely empowers the car to move.
Similarly, Atman merely enables all activities to take place. Atman is the force that enables all sense organs to perceive but cannot be perceived with the senses. Atman energises all organs of action but cannot be embraced by them. Atman enlivens the mind to feel various thoughts but cannot be felt by the mind. Atman facilitates the understanding of the intellect but cannot be captured by the intellect.
So Arjuna is not killing nor are the Kauravas getting killed. Only the ignorant think so and suffer. Just perform your karyamkarma, obligatory duty, without attachment. Do not get involved in the action.
20. This verse is taken from Kathopanisad Chapter I, Section ii, Mantra 18.
Krsna is trying to get us to shift the focus from the world to Atman. As long as your attention is on the world you will get attached and suffer. In this verse He gives pointers to Atman. It is impossible to define Atman in words. A physical experience can be described with some accuracy. Emotions are difficult to communicate. Intellectual ideas are far more difficult to convey. When it comes to Atman it is impossible as the finite cannot capture the Infinite. Hence we have to make do with indicators.
Aja – Unborn. It has no birth and no death. Beings go through the cycle of birth and death. Waves are born, they exist for a while and they die. But the ocean remains the same.
Nitya – Eternal. Exists at all periods of time.
Sasvata – Immutable. It is the changeless substratum upon which the changes in the world take place.
Purana – Ancient. Time came into being at the second experience. Atman was present even at the first experience hence beyond time.
Atman is not slain when the body is slain just as the ocean is not destroyed when the wave is destroyed.
Your focus is on the surface. You have no understanding of the truth behind the functioning of the universe. You see birth and death and are traumatised by the changes. Shift your focus to Atman. You will understand that nothing is born or is dying. The whole thing is a figment of your imagination!
Even in the world your problems stem from a limited, myopic view of things. When you get to the bottom of it the problem dissolves.