No civilisation, not even that of ancient Greece, has ever undergone such a continuous and profound process of change as Western Europe has done during the last 900 years. It is impossible to explain this fact in purely economic terms by a materialistic interpretation of history. The principle of change has been a spiritual one and the progress of Western civilisation is intimately related to the dynamic ethos of Western Christianity, which has gradually made Western man conscious of his moral responsibility and his duty to change the world.