The traditional method to arrive at Brahman is to begin with a Mahāvākyam [‘Summary Affirmation’]. It is an approach to the terminus, a pedagogic convenience, not the terminus itself [as so frequently and incorrectly extolled in the present Guru-Culture].
The earliest Mahāvākyam, [‘Summary Affirmation’], is from the Chāndogya Upaniṣad (around 1,000 BCE): Sarvam Khalvidam Brahma: ‘All [this] is Brahman‘ [3.14.1].
Variants of this theme can be found in every one of the World’s Mystic Traditions. Kurt Gödel [1906-1978] the celebrated Logician, a subject at the opposite end of the Mystic Spectrum observed: ‘Mind is everywhere is the great Mystic Teaching.’
Here, from the Christian ‘Gnostic Gospels’ [around 100 CE]: ‘You read the face of the Sky and of the Earth, but you do not recognize the one before you and you do not know how to read this moment..I am the All. The All came forth from Me…and attained in Me.’
Or the Plotinus’ ‘One’ which dominated European Mystic Schools for a millennia: ‘A Nameless Unity, indescribable, undefinable.. never known measure, stands outside number..is under no limit of any kind..is Everything and Nothing..’
OK. Now for the tricky part. 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’.
The word Brahman is ensconced in layers of self-reference, what we call the Self-Loop. It will twirl you around like a top if you don’t stay alert.
I can’t locate ‘The All’ while sitting on my rocker because ‘The All’ includes me sitting on my rocker. And it includes me thinking about locating ‘The All’ while sitting on my rocker. And…ad infinitum.
Any Inquiry into Brahman begins with the issue of the Subject. If I duck the confrontation, I will reduce Brahman to an Idea, another Man-Made ‘God’, the Immaculate Perfected ‘Being’. Which is pretty much the state of things today.