Non-duality is an extremely complex (failed) attempt to characterise what underpins the witnessing of a certain modality of experiencing that is the human condition. Current understanding has it explained as the combination of at least 3 basic but disparate parts – (1) orthodox mysticism, ie ‘behind everything is the One’;(2) everydayness is an illusion; & even better (3) duality itself is an illusion! How these ideas meaningfully cohere is itself a mystery, but not one that bothers New Age theory.
So where does the failure lie? In conflating bog standard oceanic mysticism (Böhme, Jung, Plotinus) with non-duality we inevitably have to descend into mistaken talk about ‘silence, elusiveness, boundlessness, dynamism, transcendency, vastness etc etc’ which equates with the stock in trade jargon of the ‘altered states of consciousness mystics’ like Tolle or Spira or any number of others who encourage plunging into the imagination and gratefully accepting resulting feelings of oneness & wonder. Pure metaphysics and oceanic mysticism are entirely different destinations and ought not to be confused. (Meister Eckhart was a pure metaphysician but no one seems interested in reading him that way.)
Non-duality is not oceanic mysticism about ‘the One’ or silence or stillness or the unravelled Self or a ‘something greater’; these are all dualistic characterisations appropriate to a dualistic understanding of the problem at hand.