The conventional everyday world that we live in is described in Buddhism as the world of duality, or the realm of the opposites. The Sanskrit word for this is Samsara, meaning the world of birth and death.
For our minds to be able to process our environment we divide everything up into categories: East and West, women and men, left and right, day and night, table and chair, good and bad, pleasant and unpleasant, happy and sad etc. etc. This way of viewing the world is not a problem in itself, and indeed is necessary in order for us to be able to function. It is not the case that Samsara is “bad”.
The problem arises, however, when we believe that this is how things actually are, that night is separate from day, that I am separate from you, this country is separate from another country. Then we become scared and we look at everything around us in terms of whether it will cause us harm or bring us benefit. We fight to hold on to what we believe we must have and we push away everything that we don’t like.
Buddhism teaches us to see that we are looking at the world from a relative point of view, the view that I am the subject and everything else is an object which I can act upon or which can act upon me, when in actuality such separations do not exist. If we can start to let go of this point of view, let go of our judgements and opinions, or at least accept the possibility that there is another way of perceiving the world, then we may begin to get a sense of a much deeper reality, what is known as the realm of non-duality.
When we meditate we try to put down dualistic thinking, we let go of involvement with each impression that appears in our consciousness, allowing the mind the chance to rest in the non-dual.
The Heart That Trusts to the Eternal, by Kanshi Sosan (trans. Rev. Hubert Nearman) says:
Dualities are all
what the false self deliberates upon;
They are the stuff of dreams and fantasies
or as the spots before one’s eyes
which are mistaken for flowers,
so why struggle to grab on to these
and cling to them?
Gain and loss, right and wrong:
let go of such things at once
and forget all about them
For, when the eye does not close in sleep,
all dreams cease of themselves.
When the mind does not discriminate,
all things in the whole universe
are the One Which Is.