The Enlightenment brought up a plethora of philosophical disputes, many of them concerning the place of religion. However, what is often overlooked is the radical skepticism that some philosophers concluded about our ability to have knowledge - any knowledge at all! Perhaps the most distinguished philosopher of this stripe is the late eighteenth-century deist, David Hume. Hume accepted a version of the teleological argument for God's existence, but most of his skeptical conclusions were things that even he didn't believe in practice. For example, he famously rejected the notion that we have a firm basis to believe in the law of causation, even though he himself affirmed it. In a February 1754 letter to John Steward, Hume explains, "But allow me to tell you that I never asserted so absurd a Proposition as that anything might arise without a cause." 
However, this post is dedicated to a different problem that Hume brings to our attention. This issue is known today as the "problem of induction." In our daily experiences, we use induction all the time. As I turn the knobs in my sink, I expect water to flow out in order to wash my hands. The reason I expect this is because in every past instance where I have turned the knobs, I have successfully been able to wash my hands with water. In other words, induction makes use of probability to arrive at some inference. We believe the future will be like the past.
Hume's question is this: why assume the future will be like the past? On what rational basis do we make this conclusion? It is true that we must do so in practice, but Hume and others want to know the rational foundation of this conclusion. One might suggest that we can trust in induction based on the uniformity of nature - that is, nature behaves in certain predictable ways because it has some inherent disposition toward regularity. Upon reflection, however, this explanation will not suffice. For, why do we believe in the uniformity of nature? Presumably, it is because we use induction to come to the conclusion that nature is uniform. It should be fairly obvious by now that this is nothing more than a circular argument. The interlocutor asserts that we can trust in induction because nature is uniform, but he has to justify his belief in the uniformity of nature based on his own acceptance of induction.
In my earlier posts, I referred to the uniformity of nature, but that was in the context of how we can know certain analytical truths are necessarily true (i.e. A=A is necessary true at every time and in every place). What the problem of induction raises is the issue of various physical phenomena, such as gravity or electromagnetism, which aren't logically necessary in any broad sense.
The theist justifies both the use of induction, as well as our belief in the uniformity of nature (in all its specific points) on the grounds that God created the world, and that the world reflects the order and uniformity that He imbues in it by His sovereignty. Notice that now we're not stuck in a vicious circle, but rather we have somewhat of a spiral. We are no longer arguing, "A because A," but rather, "A because B." God, who is on a higher metaphysical plane than the physical cosmos, is what provides the rational foundation for induction, according to this view.
 The Letters of David Hume, 2 Volumes, edited by J.Y.T. Greig, Clarendon Press, 1932, 1:187.