न त्वेवाहं जातु नासं न त्वं नेमे जनाधिपाः।
न चैव न भविष्यामः सर्वे वयमतः परम्।।2.12।।
But certainly (it is) not (a fact) that I did not exist at any time; nor you, nor these rulers of men. And surely it is not that we all shall cease to exist after this.
It is not that I did not exist at any time. I certainly existed. The basic idea is that even though the bodies were taking birth and dying, I was eternally present in them. Also, you and all these kings always existed eternally. Similarly we all will surely continue to exist even after the destruction of these bodies.
The idea of eternity in three times of past, present and future is with reference to the swaroopa (essential nature) of our self (=atman). The use of plural noun is with reference to the plurality of bodies and it does not indicate plurality of self (=atman). There is no multiplicity or plurality of self (=atman).
Now, Atman is eternal like what. In order to give analogy, Bhagvan says—[Next shloka discusses this]