Chapter 2, Verse 16
nāsato vidyate bhāvo
nābhāvo vidyate sataḥ
ubhayor api dṛṣṭo’ntas
tvanayos tattva darśibhiḥ
That which really is, cannot go out of existence, just as that which is non-existent cannot come into being. The end of this opposition of ‘is’ and ‘is not’ has been perceived by the seers of essential truths.
This means that everything which is limited, will be destroyed. And what is not limited, the Atma, cannot be destroyed; it is ever-existent. You will realise the eternity of the soul only when you rise above the duality of the real and the unreal. Why would non-existence exist? Non-existence is not real. By non-existence, Krishna is referring to the body and referring to all the people on the battlefield. He says, “These people are not real. They appear to exist, but they are not real. The only reality behind all this is the Self. Look beyond this duality. Perceive that which is beyond what your mind is showing you. The soul doesn’t go through these changes; in all circumstances, it never ceases to exist.” It is unchangeable.
Arjuna is feeling much grief that he will have to attack Bhishma Pita. His grief is not so much for the other Kauravas. The most important thing to him is his relationship with his great uncle. He fears that if he kills him, what will happen to his soul? In the first chapter, Arjuna says, “The ancestors will go to Hell.” So he fears that the soul of Bhishma, who is a great being, will go to Hell. Krishna tells him, “No. Bhishma Pita is as pure as the river Ganga. The purpose of his existence here is to do what I have commanded him to do. Nothing can exist without Me willing it that it exists. Everything exists because I will that it exists. But you have to see that it is My Will. If you don’t see that it is My Will, you are stuck in the real and the unreal; and you can’t distinguish between the real and the unreal. The saints and the seers, the wise ones have always reached this conclusion: everything else outside changes; but everything comes from only One Reality, which is God. There is only One Reality, My Reality, nothing else. This is the Truth. This is the essential Truth.”
Bhagavad Gita