From The Secular City: Secularization and Urbanization in Theological Perspective by Harvey Cox
If the Greeks perceived the cosmos as an immensely expanded polis, and medieval man saw it as the feudal manor enlarged to infinity, we experience the universe as the city of man. It is a field of human exploration and endeavor from which the gods have fled... The name for the process by which this has come about is secularization.
What is secularization? The Dutch theologian C. A. van Peursen says that it is the deliverance of man "first from religious and then from metaphysical control over his reason and his language." It is the loosing of the world from religious and quasi-religious understandings of itself, the dispelling of all closed worldview, the breaking of all supernatural myths and sacred symbols. It represents "defatalization of history," the discovery by man that he has been left with the world on his hands, that he can no longer blame fortune or the furies for what he does with it... It is what Dietrich Bonhoeffer in 1944 called "man's coming of age."
(I find it interesting that this was written in 1965. Yet currently in the United States there are those who contend that that state has a basis in Christian faith, and who would impose their interpretation of this faith on society as a whole, through prayer in public schools, public funding of charter schools through vouchers, illegalization of gay marriage on the basis of Judeo-Christian tradition, and teaching intelligent design as an alternative theory to evolution. Yet Cox argues in his book that the secularization of modern society has its basis in the Bible.
I personally think that "he can no longer blame fortune or the furies for what" man does with the world is a very important statement. Many people today believe that their actions are predetermined by God: if they do something wrong, then the Devil tempted them to do it. I tend to think that neo Calvinist thought like this is dangerous because it strips man, the thinking animal, of his moral responsibility.)