Non-Duality is about reality as it is, one undivided whole. Duality is for the mind while reality transcends the mind. Duality is a way of perceiving, and not the truth of the whole.
The truth of the whole is neither one nor two. It is simply what it is. Non-Duality is just a way of negating the common held worldview that is characterized by duality.
Me and you, this and that, him and her, love and hate, etc. Yes of course these interrelated opposites are true in a sense or rather from a certain place of looking, but the deeper and more profound seeing is not concerned with these divisions.
Your Nirvanic Eye is always one, seeing totality. A formless eye that gives birth and witnesses all things simultaneously.
This is the peak of spirituality.