In this book, Berdyaev tells us that the creative development of the spirit and the free exercise of man's powers can be conceived only as the free cooperation of man with the work of God. Creative spiritual development represents a new principle which signifies an offering of human freedom to God, an offering which God expects from us. The life of the spirit is a creative and dynamic process. Spiritual development is possible only because there is freedom. Spiritual development is not movement on the plane of the external world, but the bringing to birth of forces which lie hidden in the inner depths of existence. To quote Berdyaev, "the spiritual world is like a torrent of fire in free creative dynamism." The Russian philosopher Nikolai Berdyaev (1874-1948) was one of the greatest religious thinkers of the twentieth century. His philosophy goes beyond mere thinking, mere rational conceptualization, and tries to attain authentic life itself: the profound layers of existence that are in contact with God's world. Berdyaev directed all of his efforts, philosophical as well as in his personal and public life, at replacing the kingdom of this world with the kingdom of God. According to him, we can all attempt to do this by tapping the divine creative powers which constitute our true nature. Our mission is to be collaborators with God in His continuing creation of the world. This is what Berdyaev said about himself: "Man, personality, freedom, creativeness, the eschatological-messianic resolution of the dualism of two worlds - these are my basic themes."