6 “And God saw that it was good.” Scripture does not merely wish to say that a pleasing aspect of the sea presented itself to God. It is not with eyes that the Creator views the beauty of His works. He contemplates them in His ineffable wisdom. A fair sight is the sea all bright in a settled calm; fair too, when, ruffled by a light breeze of wind, its surface shows tints of purple and azure,— when, instead of lashing with violence the neighbouring shores, it seems to kiss them with peaceful caresses. However, it is not in this that Scripture makes God find the goodness and charm of the sea. Here it is the purpose of the work which makes the goodness.
In the first place sea water is the source of all the moisture of the earth. It filters through imperceptible conduits, as is proved by the subterranean openings and caves whither its waves penetrate; it is received in oblique and sinuous canals; then, driven out by the wind, it rises to the surface of the earth, and breaks it, having become drinkable and free from its bitterness by this long percolation. Often, moved by the same cause, it springs even from mines that it has crossed, deriving warmth from them, and rises boiling, and bursts forth of a burning heat, as may be seen in islands and on the sea coast; even inland in certain places, in the neighbourhood of rivers, to compare little things with great, almost the same phenomena occur. To what do these words tend? To prove that the earth is all undermined with invisible conduits, where the water travels everywhere underground from the sources of the sea.
Source: Nine Homilies of Hexaemeron (New Advent)