Augustine on Miracles

Miracles. Since God made the world, he can intervene in it (see <a href="http://www.crossbooks.com/book.asp?pub=0&book=2697&sec=00007181#Miracle">Miracle</a>). In fact what we call Nature is simply the way God regularly works in his creation. For, "when such things happen in a continuous kind of river of ever-flowing succession, passing from the hidden to the visible, and from the visible to the hidden, by a regular and beaten track, then they are called natural." But "when, for the admonition of men, they are thrust in by an unusual changeableness, then they are called miracles" (On the Trinity, in Nicene and Post-Nicene Fathers, 3.6). But even nature's regular activities are the works of God. For,

Who draws up the sap through the root of the vine to the bunch of grapes, and makes the wine, except God; who, while man plants and waters, himself giveth the increase? But when, at the command of the Lord, the water was turned into wine with an extraordinary quick-ness, the divine power was made manifest, by the confession even of the foolish. Who ordinarily clothes the trees with leaves and flowers except God? Yet, when the rod of Aaron the priest blossomed, the Godhead in some way conversed with doubting humanity, [ibid., 3.5]

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Baker Encyclopedia of Christian Apologetics.