Dan, I’m loving having these conversations with you – especially since your questions and thoughts are so stimulating. Before getting into the nuts and bolts just a brief response to your comment on the meaning and purpose of life. As I hope you know, I certainly do not think your life is without meaning and purpose. My point was simply that Christianity imbues life with a particular meaning and purpose – that faith becomes a driving force in life.
Your last post was probing, and to provide a short answer will be impossible. But stick with me and I shall make things as brief as I can. First I do need to dispute your definition of miracle. For Christians, miracle could never be limited to that outside the laws of nature, because that would prevent us from celebrating the hand of God in and through nature. This fact is, I think, recognised even by some scientists. Cosmic physicist Paul Davies describes the likelihood of life in the universe in terms of our having won the ‘cosmic jackpot’: “If almost any of the basic features of the universe, from the properties of atoms to the distribution of galaxies, were different, life would very probably be impossible. Now, it happens that to meet these various requirements, certain stringent conditions must be satisfied in the underlying laws of physics that regulate the universe, so stringent in fact that a bio-friendly universe looks like a fix – or ‘ ‘put up job’ … as if a superintellect had been monkeying with the laws of physics.”
Many people (including many Christians) think that God is constantly intervening in the laws of nature to bring about his purposes. Thus, people presume that to locate God we need to do so in those things that cannot be explained by science. Yet as Davies also notes “A God who lurks in the dark corners of human ignorance is a God who must make a slow and inexorable retreat as science progresses.” In fact the church founded universities precisely because they understood that God was the primary cause of nature, so that an exploration of nature is one into the wonders of God.
This is a vital point. Christian tradition understands God as the primary cause of all secondary causes. He is not one cause among many. We do not say ‘this thing cannot be explained by a natural cause therefore it is God’. Instead we recognise that God is at work in all secondary (I.e. natural) causes. He does not just start up the world and leave it to its own devices but he sustains and lies behind all that is.
So, I’m a firm believer in miracles but I do not believe that God breaks natural laws all that often (although no doubt he can and sometimes does). Such would actually undermine his power, since it would suggest that the creation is somehow deficient -that it needs tinkering around the edges to be effective!
So, what then is a miracle? It is something that causes people to recognise the wonder of God. It is a sign that points to the providential goodness of God . This may be the “miracle of nature”, such as the miracle of the human body. This may be the miracle of circumstances – when each individual event has a ready enough natural explanation but there is a miraculous confluence of events (e.g. Jesus calming of the storm; storms always go calm – just not always in response to prayer!). This may be something extraordinary that cannot be explained by science now – even if one day it might. My close friend Neil Ormerod notes that there have been recent discoveries of the way in which bacteria have brought about instantaneous cures of certain cancers. This observation, however, does nothing to reduce the miraculous experience of a person who receives such a healing after prayer; nor does it eliminate the work of God in that healing – as I’ve already suggested, the opposite is true.
Clearly, I am not as sceptical of science as many of my Christian friends. In fact, I am a passionate amateur scientist who reads cosmic physics in my spare time. Having said this, nor do I give science the ultimate authority that you seem to give it. Science cannot and never will be able to explain everything. This is not only because of the limitations of human knowledge and human capacity. It is also because the universe, and God at work in universe, is spectacularly mysterious. Science does a good enough job of explaining certain phenomena, but there is so much that is beyond its reach. Because this is so, I actually am sure there are miraculous events that simply cannot and will not ever be explained by science. Given my earlier arguments I will not be in a position ever to be able to say categorically that this or that event has no natural explanation, and since God is at work in nature I do not need to. Yet I am also open to God transcending nature, and I think that is a perfectly rational position to take. Christian faith then is not irrational.
PS – my insights into these questions have come from ongoing conversations with my friend Neil Ormerod. But they are not unique to he and I. They are in fact the standard theological responses of mainline church thinkers such as Augustine Aquinas etc. That is to say these are not heterodox views but long-standing orthodox ones.
PSS – I have not directly answered your question about God healing a cataract rather than healing leukaemia or fixing the problems of poverty in Africa. Will do so in another post
PSSS – sorry to all of this lengthy confusing post!
 Davies, Cosmic Jackpot , 3-4.