“A common characteristic of many mystical states is the presence of a consciousness of the Oneness of everything. All creaturely existence is experienced as a unity, as All in One and One in All. In theistic mysticism God is felt to be in everything and everything to exist in God.
In ancient Chinese philosophy the creation of the phenomenal universe is envisaged as coming out of Tao, the Primal Meaning and Undivided Unity behind everything, by the pulling asunder of polar opposites. Out of Tao sprang the principles of phenomenal reality, the two poles of yang (light) and yin (darkness), which are evident throughout the whole of the universe as it appears to us. We cannot conceive of light except as the opposite of darkness, of above except as the opposite of below, of before except as the opposite of after, of goodness except as the opposite of evil. Our perception is conditioned by the existence of these polar opposites. Yet, they are only active in the realm of phenomena.
In this realm of polar opposites man is imprisoned. He is conscious, therefore, of a division in his soul. His deepest spiritual instinct is to break through the polar opposites and find again the Primal Meaning, so that he may once again be restored to the Undivided Unity which he has lost.
God is to be found, said Nicholas of Cusa, beyond ‘the coincidence of contradictories’. There can, however, be no escape from duality through sense perception, for sense perception is conditioned by the presence of polar opposites, nor through discursive thought, which is bound by the same dualism. For to the mystic is given that unifying vision of the One in the All and the All in the One.
There is little doubt that this sense of the Oneness of everything in the universe and outside it is at the heart of the most highly developed mystical consciousness. All feelings of duality and multiplicity are obliterated, including the duality between man and Deity. Though it may be expressed differently, this is equally true of Hindu and Sufi mystics, of Plotinus and of the great contemplatives of Christianity.”
F.C.Happold, Mysticism, Penguin 1965