The further we study the phenomenon of deep sleep the more we shall come to understand the mystery of life. It gives a key to the mystery of life, because it is an experience of consciousness which divides our spiritual consciousness between the physical and the spiritual world. It stands as a barrier between two experiences: one in this world and one which is reached by spiritual attainment. Our great poet of Persia, Rumi, who has inspired millions of people and whose works are considered in the East as the foundation of higher knowledge, has written about sleep: