I acknowledge this graphic from the Net
Self is eternal, indestructible, unknowable
Its manifested bodies have an end
Fight therefore, Arjuna
Krishna makes a clear distinction between the real and unreal, manifest and unmanifest, and transient and permanent in this verse. This verse in a way encapsulates all that Krishna said before and says later.
Krishna distinguishes between Self and self. Self is real; self is transient. Self is the spirit and the energy that is forever, whereas self is the mind body that perishes with the last breath we take. Self, as Krishna says, is eternal. What does eternal mean? Nitya, the Sanskrit word used here is usually translated as eternal or always. When something is considered eternal, it does not have an end. Does it then have a beginning? When something cannot be destroyed, was it ever created? Anything that is created has an end point by the law of nature. All matter perishes.
When manifested bodies, the mind bodies that you and I occupy come to an end, what then happens?
Even science has an answer to it today! Matter converts to energy when it comes to an end. Energy has no end. Energy is eternal and indestructible. The opening verse of the Upanishads, the first verse of Isa Vasya Upanishad, says all that exists is energy. The mind body has an end as matter. When that end comes it converts into energy and becomes eternal. It may or may not return as matter, and even if it does the cycle back into energy will continue. Energy can neither be created nor destroyed.
Krishna says that this energy is unknowable. One may say that one feels energy or feels energetic, when the energy is manifested in the mind body, or any other matter in one form or another. The underlying energy itself is not perceived by the senses. As a result is is not interpreted by the mind. What the mind does not cognise is not knowable. In one sense, we never know what energy form the mind body will take when it comes to an end is unknown. All talks about reincarnation is hypothetical. When the energy itself is unknown, how can one predict the material form it may take again?
Finally, Krishna says to Arjuna to fight on.
This verse is the answer to Arjuna’s dilemma of whether he should fight and kill his kinsmen, thereby incurring sins, or fight regardless as his dharma as a kshatriya. Krishna here does not address either part of the dilemma. He does not talk about kshatriya code of conduct or about whether following that will attracts sin. He cuts the root of those arguments by questioning Arjuna about what he is destroying by killing his kinsmen. He says simply that when the manifested bodies come to perishable end, the matter converts into something eternal. So, nothing gets destroyed!
This is also one of the most controversial verses of the Gita from a societal perspective. What Krishna says is the natural law, which all animals obey and act upon. Human societal laws are artificial, designed to create an organised, civilised society. Where do these two laws, the natural and the societal meet, if at all?