'God is always at work, but that work is not always visible. God is always at work, but sometimes the world's processes go with the grain of his final purpose and sometimes they resist. But if certain things came together in the world at this or that moment, the 'flow' would be easier and more direct. Perhaps a really intense prayer or a really holy life can open the world up that bit more to God's purpose so that unexpected things happen.'
Rowan Williams on miracles in his excellent little book of introduction to Christian belief. Click on the image, or the title link, to by from Amazon. Good quiet day book. Most of the paragraphs reveal more if you read them twice.