The theory of Tawhid (Unity of Divine Being) has been beautifully expressed by the Persian Sufi poet Farid ud din Attar (1157-1235) in his Mantiq utTair or the Conference of the Birds.
It is a poetic rendition of the consequence of an assembly of the birds of the world who begin their search for their ideal king, the Simurgh. The birds believe their the king to live beyond the mountain of Kaf that surrounds the world. Thousands of birds are lead by the magnificent Hoopoe in this Quest. They cross an endless desert, then the Seven Valleys of Understanding and meet slaves, princesses, hermits and creatures on the way. They learn to confront their fears and once the astonishing landscapes are behind them, just thirty birds reach the end of the journey. To their astonishment the King is none other than themselves and the birds are transformed in to the great unknown bird, the Simurgh resolving the enigma of I and Thou forever. There in the Simurghs radiant face they saw. Themselves, the Simurgh of the World- with awe. They gazed, and dared at last to comprehend
They were the Simurgh and the journeys end
They see the Simurgh- at themselves they stare
And see a second Simurgh standing there