You will come across many teachings about the 'error' of duality, and the need to overcome it, to achieve Oneness. I understand that idea, and the insistence of overcoming duality, a natural and to my mind, necessary state that has been corrupted to mean separateness ... that we are discrete, separate beings inhabiting a world of separate objects: the I-It condition described by philosopher Martin Buber, in which the other is always objectified, rather than the integrative I-Thou perception that fosters mutuality and connectedness . So wanted to explain a little my understanding and experience of Oneness.
I don't see Oneness as many others do, as superior to, or more spiritual than the Many, for the Many are infinite expressions of the One, each necessary to the existence of the world, in the same way that the infinite variety of sounds are necessary for the creation of bird song, the cricket's buzz, for the manifestation of music. Music is not something independent of notes or sounds: it is the manifestation of their relationships to each other. In the same way, the One is both the generative source and the infinite manifestation of diverse relationships between All Things.
Without the many, the world that we know or can create could not be. Without the One, nothing could be.
I think that that's what the goddess was telling to Parmenides on his journey into the otherworld, "that being is without beginning and indestructible; it is universal, existing alone, immovable and without end; nor ever was it nor will it be, since it now is, all together, one, and continuous ..... [and] all is full of being; therefore the all is continuous, for being is contiguous to being."
Being at One, developing Oneness thinking, therefore, does not to me imply a rejection or diminishment of our sacred individuality, or an ultimate spiritual goal of reuniting with and melting into the original One. I'm with Marie-Louise von Franz who declared that dissolving into Oneness had no appeal to her if she could not experience it as herself.
What is required, it seems to me, is to hold the apparent opposites of Oneness and multiplicity in tension, as Jung said of integrating the different aspects of our psyche; to see them as a continuum along which we might be at different points through our lives ... sometimes closer to a felt experience of Oneness, sometimes deeply focused in a particular moment of our individual being, more often, one hopes, consciously aware of being balanced between Oneness and individuality and recognising the sacredness of it all.