I am only referring to that sentence, which is the most famous one, and which is most central. The Knowledge that you gain by Jnanayoga is fundamentally this: that which exists, exists, that which does not exist, does not exist. Of that which exists, it can never have non-existence. That which does not exist, of that, that can never come about an existence.
This “existence”, in other words is something different from “manifestation”. In manifestation, that which exists ‘now’ ceases to be tomorrow or thereafter, any moment. And that which manifest did not exist one minute ago, one second ago. Therefore, when you arrive at true Knowledge, you are able to make a distinction between the “existence”, and “manifestation” so that you become free from the arresting concentration in which you are involved in manifestation. All the time, we are engaged in manifestation where things are born and things die.
As Sri Aurobindo says that, “The movement of manifestation is so rapid that things seem to pass away even before we observe them.” It is a fleeting movement of manifestation, and things come to manifest, and before you can even grasp, they are gone. Some new things have come up immediately.
What Sri Krishna wants to say is that, “If you want to deal with life properly, you should be able to come out of arrest of manifestation, and go back, or go behind and discover what really exists. And that which really exists can never cease to exist. And that which does not exist can never come into existence.”
If you apply this sentence to manifestation, you will find that that which did not exist, comes into existence; that which exists goes out of existence. Therefore, it means that that which manifests is not ‘really’ existent: it is something different. That is why manifestation is called phenomenon. That which exists is called essence: that which is essence always remains; essence can never die. The distinction between essence and phenomenon is what is called Sankhya knowledge: Sankhya knowledge is the knowledge of discrimination, distinction between essence and phenomenon. Normally we do not see anything that does not manifest: that means that we are arrested in a state, which is not the state of Knowledge.
There is a beautiful dialogue in Plato’s book called “Republic”. You know, “Republic” is supposed to be one of the greatest works of intellectual thought in the world. The climactic point of intellect is supposed to be reached in this book called “Republic”, where the main speaker is Socrates: it is a dialogue between Socrates and many others.