I have talked with a couple of people lately who have mentioned oneness, and it reminded me of how this too looks differently depending on the center of gravity of identification and the whole aqal context as well.
Identification with a segment of the seen: oneness as emotional merging or a taste
When there is an exclusive identification with our human self, the idea of oneness typically remains just an idea. We may try some form of emotional merging, or feeling into the oneness, but that is about it. It does not go very far, and typically includes effort and fantasy.
Sometimes, there can also be a taste of oneness when I is temporarily forgotten (or more precisely when the idea of I is forgotten - and there is not the attachment to or building up of the idea of I). The sense of I goes into the background or falls away for a while, revealing all there is as a seamless whole. This can happen through sex, drugs (food, alcohol, recreational drugs), rock'n roll (entertainment) and relaxation (meditation, receiving Breema).
Identification with the seeing: the world of form as a seamless whole
When the center of gravity shifts out of the seen and into the seeing, when we find ourselves as pure awareness, as Witness, as that which the seen arises to and within, oneness takes a different form.
Now, the seen is revealed as an always a seamless whole, as one if you like.
This human self appeared as inner and the rest of the world as outer, and now, inner and outer is revealed as created by the exclusive identification with our human self. It is not inherent in the world of form.
The whole world of form arises within and to awareness, as a seamless always changing whole. It is one.
Noticing that seeing and seen are not two: a taste of oneness of seeing and seen
After a while (or sometimes right away) there is the noticing of the seen as arising to, within and now also as awareness. The seeing and the seen are both awareness. The seen are not so different from the seeing. They are not two.
The boundary between first I as seen and Other as seeing, and then I as seeing and Other as seen, now starts to erode. It is the early realization of the absence of I anywhere. The sense of I is merely created by an attachment to the idea of I as a segment of what is. I and other are not inherent in neither the seeing nor the seen.
Here, there is a taste of the oneness of seeing and seen.
Absent of I: absent of oneness and manyness, yet including both
The next shift is into realized selflessness.
Here, the inherent absence of I in seeing and seen is fully realized.
The Ground of seeing and seen is inherently absent of oneness or manyness, yet also allows and includes both.
That is why the whole game of hide and seek could play itself out in the first place: from exclusive identification with the seen, with the human self, to include - or shift to - the seeing itself, to a hunch of the absence of I anywhere, to realized selflessness.