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.
Shūnyam is its direct and only descendent.
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’.
Now Brahman is an ancient and venerable word and best left on the altar. Instead I shall replace it with the more mundane: ‘Everything’.
So how do I go about locating ‘Everything’? 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’.