For how can an event by contrary to nature when it happens by the will of God, since the will of the great Creator assuredly is the nature of every created being? (City of God 21.8)
While this somewhat recapitulates my summary, it takes things a step further. It is not just that all things willed (created) by God are natural because creation itself is nature, natural, but that God's will is the nature of all created beings: it is not that God's will wills creation, but God's will is creation. This resonates with Genesis 1 where God speaks and it is. God's will cannot be fruitless or without consequence, but always occurs. If God need only speak or will and what God speaks/wills is, then what is is God's will. This, however, is just a mind-teasing introduction to the actual line that caught my attention in this seemingly endless opus by Augustine; a line on the naturalness of portents based upon our own lack of knowledge:
A portent, therefore, does not occur contrary to nature, but contrary to what is known of nature. (ibid.)
A post-Enlightenment rationalist or empiricist could not say it better. What seems as an unnatural occurrence is natural; its unnaturalness merely reflects our lack of knowledge of how the natural world works. This sounds a lot like the modernist scientific (although undoubtedly not a view shared by all) characterization of religion as taking care of what science cannot yet explain, but, most interestingly, it does so from the opposite perspective, since what we cannot know is how miracles naturally work, what laws of nature govern miracles, omens, and portents. While the one perspective uses this to dismiss the miraculous (since in modern definitions, the miraculous is contrary to nature), the other uses it to affirm it as the most natural thing; and these laws that govern nature are, themselves, the very will of God.