The much quoted text, My kingdom is not of this world (John 18:36) does not mean that the kingdom is not, or will not be, in this world or on this earth. … When Jesus and his disciples are said to be in the world but not of the world, the meaning is clear enough. Although they live in the world they are not worldly, they do not subscribe to the present values and standards of the world. … The values of the kingdom [of God] are different from, and opposed to, the values of this world. There is no reason for thinking that it means the kingdom will float in the air somewhere above the earth or that it will be an abstract entity without any tangible social and political structure.

p. 48. - Jesus Before Christianity: The Gospel of Liberation (1976)