Alongside Rig Veda 1.164.46, 10.90.2, part of the famous Purusha Sukta, is one of the most succinct declarations of Advaita in the Vedas. It goes further than 1.164.46, as it gives a name to ‘what is one’ – Purusha (the Self). It says,

It is the Self who is all this – whatever has been and whatever is to be.

We could easily mistake this for a mantra from the Upanishads or another Advaita text, as it is perfectly in-line with their teachings. For this reason, it is unsurprising that it later appears in the Upanishads, in Shvetashvatara 3.15.

We can understand the significance of ‘Purusha’ more when we look at some of its etymological derivations. The Brihadaranyaka Upanishad explains,

1.4.1. Since, before (purva) all this, he burnt up (us) all the evils from everything, he is Purusha.

2.5.18. This person (purusha) is lying in the citadel (purishaya) in all citadels. There is nothing that is not covered by him, nothing that is not surrounded by him. [1]

Both mantras echo Rig Veda 10.90.2  – “before all this” and “nothing that is not covered…not surrounded”, are the same declarations as Purusha is “all this – whatever has been and whatever is to be.” It’s worth noting that ‘puri‘ has the double meaning of city and body. So, Purusha “lying in the citadel” means residing in the body and, “in all citadels” means in all bodies [2]. In Shankara’s Mandukya Karika Bhashya, he explains that the Purusha manifests all the jivas and that they are inseparable, it like sparks and fire or how all of the reflections in the water are of the same sun [3].

The first mantra of Mandukya Upanishad is almost identical to Rig Veda 10.90.2, replacing ‘Purusha’ with ‘Om’,

The syllable Om is all this; it is a symbol for what was, what is and what shall be.

Om as “a symbol for what was, what is and what shall be” means Brahman or Purusha. Akshara, “syllable”, has the double meaning of “imperishable, eternal”. It is synonymous with Om because Om is the eternal syllable or sound. This means that. “The syllable Om” equally means “The eternal Om”. The eternal Om is “all this”, as what Om “is a symbol for” (Brahman) is eternal.

Akshara and Om point to the reality that Brahman is every syllable and all sound. For this reason, Shankara declares that Brahman is known through Om alone [4]. Om is  likened to a boat carrying one across the sea of Samsara to the ‘shore’ of liberation in Maitri Upanishad (6.28). The purpose of a mantra is, similarly, to realise Brahman through the power of sound and vibration. One whose mind is successfully freed through mantra has developed such concentration that they can hear Om and realise Brahman.

This knowledge is contained within Rig Veda and Mandukya Upanishad’s statement, “all this”. One who knows every syllable of a mantra, speech in general, and all sound as Brahman, have realised Om as akshara and the true meaning of Shruti – “what is heard”. ‘This’ refers to all that can be experienced, all that is perceivable. Everything we see is ‘this’ Purusha. Equally, it is Purusha that is perceiving, as the seer and what is seen are ultimately one. The mantras teach us that, aside from embodying it themselves through their knowledge, the essence of Advaita is in a single word or even syllable.

[1] Roebuck’s translation
[2] This understanding of the body as a city is found elsewhere in the Upanishads. For example, Chandogya Upanishad (8.1.5), states that the Self is located in the ‘city of Brahman’.
[3] Shankara’s Bhashya Mandukya Karika 1.6
[4] Shankrara’s Bhashya Mandukya Upanishad 1