Krishna begins laying the foundation. There was never a time, he says, when I did not exist. Nor you. Nor any of these kings standing on this field. And there will never be a time when any of us cease to exist. The soul is not something that appeared at birth and disappears at death. It has always been. It will always be.
Consider how radical this statement is in the context of a battlefield. Arjuna is terrified of causing death. Krishna responds: death, as you understand it, does not exist. You cannot destroy what has always been. These kings, these warriors, these elders you fear for — their essential being is beyond the reach of any arrow.
Krishna includes himself in this declaration — 'I too have always existed.' He is not speaking from above the human condition. He is placing himself within the same eternal framework as Arjuna and every other being present. The teaching applies to all, without exception.