Theologian Wolfhart Pannenberg made some good points in a short article on miracles; see excerpt below:
In the modern history of the dispute between scientists or philosophers calling upon the authority of science on the one hand and Christian theologians on the other, the concept of miracle has become one of the more intricate problems, because miracles are said to involve a violation of the laws of nature, as David Hume asserted in the section on miracles in his Enquiry Concerning Human Understanding (1748). This is a self-defeating notion of miracle, of course, because the logic of the concept of natural law requires that there be no exceptions–otherwise the pretended law in question would turn out not to be truly a law of nature. The concept of miracle as a violation of natural law subverts the very concept of law and in effect exposes the futility of the assertion of miracles.
This is not the meaning of the concept of miracle in Christian theology, however. In the biblical writings, the word miracle refers to extraordinary events that function as “signs” of God’s sovereign power. Therefore, the biblical language often speaks of “signs and wonders’ (Daniel 6:27; John4:48). A wonder, or miracle, is basically an unusual–in fact, extraordinary–event. Augustine said, “Whatever is unusual, is a miracle”…. Explicitly he emphasized that events of that type do not occur contrary to the nature of things. To us they may appear contrary, because of our limited knowledge of the “course of nature.” But God’s point of view is different, because he is the Creator of the nature of things as well as of the events that appear unusual to us. …
In medieval theology the conception of miracles changes, because the nature of things was now conceived of objectively, not in relation to the limitations of our knowledge. …
Later, the view of miracles as occurring contra naturam [against nature] became more generally accepted, as did a concept of nature and of the order of nature based on human experience. This development finally led to the idea that a miracle is a violation of the laws of nature.
…
The concept of miracle in the Augustinian sense of the term, then, does not involve any opposition to the order of nature described in terms of natural law. It only requires us to admit that we do not know everything about how the processes of nature work.
Zygon, vol.37, no.3 (Sept. 2002), 759-762