The earliest Mahāvākyam, summary capture of primal Vedic Truth, is from the Chandogya Upaniṣad (3.14.1; around 1,000 BCE) :
Sarvam Khalvidam Brahma: ‘All [this] is Brahman‘. Brahman is from the root ‘Brh‘: ‘To Uphold, Support’. Brahman is: ‘That which upholds’.
It was originally a Mantric expression for Yagnic formalities before it took on conventional lingual meaning.
What is Brahman? I don’t know. In fact I can never know what Brahman is. And why not? Because I am part of this ‘All’, whatever this ‘All’ is. Else it wouldn’t be the ‘All’.
So how do I go about locating Brahman? There is a problem. A big problem. And what is the problem?
I can’t locate ‘Everything’ while sitting on my rocker because ‘Everything’ includes me sitting on my rocker. And it includes me thinking about locating ‘Everything’ while sitting on my rocker. And…ad infinitum.
I can’t in other words, apply my well-worn contact-lenses that nicely repackages the world along the ‘Subject-Object Divide’, something I need to do in order to say anything about anything.
With ‘Everything’ that option is nulled.
If I want to get to ‘Everything’ I need to create a perch from which I can get a good look at it. I need something that requires a leap from the limit of abstraction. Something called ‘True Nothing’.
Here’s a clip I wrote once about the origins of Self-Reference in Classical Logic:
‘In looking for ‘Nothing’, you must remember to exclude any sensory, cognitive or affective representation of it as Object. ‘Nothing’ is radically exclusive.
In looking for ‘Everything’, you must remember to include the Looking-Subject. ‘Everything’ is radically inclusive.’
The Symbol ‘0’, the original Self-Negating Expression, is a synthetic construct that was put together with the very specific objective of helping the investigator get to the bottom of all this.
In particular, this ‘I’.