Bhagavad Gita Chapter II : Verse 35

Anyways you will be laughed at!

Bhayadranaduparatam Mamsyante Twam Maharathaha
Yesham Cha Twam Bahumataha Bhutwa Yasyasi Laghavam

Krishna now pokes Arjuna with the stick of a possible ridicule. He says all the great charioteers will think that you turned around and ran away from battle out of fear. You, Arjuna, who have been the object of respect owing to your victory in wars, will be considered as one too easy to defeat in war if you back out now, he taunts Arjuna now.
-Swahilya Shambhavi

Bhagavad Gita - Chapter 2: Verses 24-25

Cannot be cleaved, know this
Acchedyoyam Adahyoyam Akledyoshoshya Eva Cha
Nithyas Sarvagatah Sthanuhu Achaloyam Sanathanaha
(chapter -2, Verse 24)
Avyakthoyam Achinthyoyam Avikaryoyamuchyathe
Tasmadeva Vidithvainam Nanushochitumarhasi
(chapter -2, Verse 25)

The consciousness cannot be cleaved, it cannot be burnt, cannot be made wet, nor can it be dried. It is eternal and everywhere. It cannot be moved. It is motionless and has always existed and will ever exist. Consciousness is not any manifestation of thought, words or actions. It cannot be conceived by the mind. Sri Krishna says that "it is said that it cannot be modified." He then tells Arjuna, "Therefore, having known that this consciousness is the eternal truth of everything and person, one should not mourn in this manner," (referring to his sorrow over having to kill his cousins, friends and teachers in the war.) - Swahilya Shambhavi (swahilya.soulmate@gmail.com)

Bhagavad Gita Chapter 2 Verse - 22

Know the Invincible

Veda Vinashinam Nithyam Ya Enam Ajam Avyayam
Katham Sa Purushah Partha Kamghatayati Hanti Kam
*****

For the one who knows his essential being called consciousness which is indestructible, eternal, unborn and of one contiguous piece, how can such a person kill or be killed.
Sri Krishna is a mastermind here who simply draws from the whole universal truth and philosophy to achieve his aim of getting Arjuna to fight. So verse after verse, he goes into the depths of consciousness and points out to him that every creation is covered by the same consciousness and contains the same consciousness. So there is no difference here between the killer and the killed.