O Partha, considering that the individual unit of consciousness is eternal, unborn, imperishable and indestructible, how can a person kill anyone, and whom does he kill?
Bhagavad Gita - Chapter 2 - Sankhya Yoga - The Yoga of Analysis
tatha sharirani vihaya jirnany-anyani samyati navani dehi Just as one removes old clothes and accepts new ones, similarly the embodied unit of consciousness gives up old bodies and accepts new bodies.
Weapons cannot cut the individual consciousness; it cannot be burned by fire; water cannot wet it and air cannot dry it.
It is indestructible, incombustible, insoluble and cannot be withered. It is eternal, all-pervading, unchanging, immovable and primeval.
It is said that it is imperceptible, inconceivable and immutable. Thus, understanding the nature of individual embodied consciousness, it is inappropriate for you to lament.
Even if you believe that the individual consciousness is eternally subject to birth and death, still you have no reason to lament, O mighty-armed one.
For one who is born, death is certain. For one who is dead, birth is certain. Therefore, you should not grieve over that which is inevitable.
O Bharata, all living beings are unmanifest before birth, manifest between birth and death, and again unmanifest after death. What then is the reason for lamentation?
Some consider the individual conscious unit as astounding, some describe it as astounding, others hear of it as astounding – and some, even after having heard about it, have no knowledge of it.
This individual unit of consciousness dwells within the bodies of every living being, O descendent of Bharata. Thus, you should not lament for anyone.