At one point, we come to realize that oneness and selflessness are a world apart.
They may seem similar from a distance, but when we have a taste of each, we see how profoundly different they are from each other.
Oneness is a sense of being one with all, with God, life, oneself, others. There is a realization, either a seeing or feeling, of all being cut from the same fabric, maybe of all being God. A veil is lifted. The boundary of I and Other, placed within content, is softened or becomes more transparent. It is all one, one field, one substance, one life, one consciousness. Yet, there is still and I here that sees this, experiences this, is one with everything else. There is still a sense of center, of being a drop one with the ocean. The basic sense of I and Other is still present. There is still a doer around.
Realized selflessness is quite different. Here, the basic sense of I with an Other is lifted, seen through, seen as just coming from a thought. The whole world of content is a seamless field as before. It is all consciousness, as before. It is all God, as before. But now, there is no center. No hint of an “I” that has even a subtle “Other”. It is the ocean awakening to itself as the ocean, even as the drop is still living out its life. This human self and everything about it is living its own life, revealed as already and always free from a doer.
In one way, the two are not so different. They are both an awakening of the field to itself, tasting all as God.
In another way, they couldn’t be more different. One retains a basic sense of I with an Other. The other sees through it thoroughly. One has a center, the other does not.
And of course, the content of awareness doesn’t have to change for either to happen. There is still all the sensory inputs from this human self. Still thoughts, as before. Still pain and joy. Still this human self living its life, doing its things in the world. No (major) changes here are needed in either case. It all has to do with the lifting of the I-Other boundary, or rather, with a release of identification from it. A clear seeing of it as just being thought-created.