Something happened, though, as Christians began to investigate God's world. They started to discover more and more things in nature they had assumed were a result of a divine agency were really responding to laws of nature and biology and by altering the circumstances or the variables they could change the outcome of those processes. At the same time, they made great advancements in mathematics and they reawakened to the philosophy of Plato and the Greeks, which emphasized logic being the ultimate guiding force of knowledge.
Because so many achievements were coming from men thinking hard about their world, philosophers began to conclude that the ability to reason was all they needed in order to know everything there is to know about the world. Many believed God existed, but they felt that God's revelation was unnecessary for discovering truth. They assumed that given enough time and thought, man would figure it all out on his own. God was removed from being the primary source of truth as people became convinced that they were smart enough to discover anything with enough thought and analysis.
Naturalism: "God Doesn't Count as Knowledge"The removal of God as the primary source of truth was a huge shift in thinking for the world. If all people need to discover truth is to identify facts and reason through them with a good mind, then focusing on nature becomes more important and focusing on God less so. Thus the Grand Story in western society shifted from God to Nature itself, just as Romans 1:25 warned. Therefore, since God wasn't needed to understand the ways of the world, many educated people took the next step and denied Him altogether. If God doesn't offer any explanations to the ways of the world, why assume one needs to worry about Him? The worldview adopted by those who think this way is called "naturalism". The world is seen in purely mechanistic terms: this causes that just because the laws of the universe work that way.
Naturalists, because of their worldview, now seek to explain everything without pointing to God at all. Even in big issues, such as the origin of life on the earth, God cannot be accepted as a cause, because it violates their notion of "really" explaining things. Therefore, Darwinian evolution becomes the capstone in the search for a purely mechanistic way to explain how the diversity of life arose on the planet. In fact, to say "God did it" is seen as a cheat; naturalists would object to anyone claiming the involvement of a divine being saying the person hasn't thought hard enough about the problem. They define knowledge of God as false knowledge.
You can see how important it is to understand worldviews! Since naturalists are committed to not accepting explanations that involve God, their minds are closed to the existence of God before you even give evidence. The bias of naturalism is plainly seen everywhere today, even in popular culture. Gene Roddenberry, the creator of Star Trek, held to this view, and one of Star Trek's recurring themes is the evolution of man to his betterment.2 No religious belief system is ever in view for the show's protagonists. Roddenberry believed reason alone would catapult mankind into this new utopia and his popular franchise has continued to preach his message ever since.
2. See Bronislaus B. Kush' article "‘Star Trek' franchise an homage to humanist philosophy" in the Worcester Telegram and Gazette http://www.telegram.com/article/20100622/NEWS/6220371/1011