This psalm evokes the recurrent Biblical images of chaos-sea and order-walls, exploring the theme of boundaries. Images of roaring waters are associated with raging warfare, emphasizing destruction and chaos. Waters are tied to chaos because they are unbound, primeval, disorganized--water is the ferocious and impassive source from which creative life springs. The story of Yahweh and the sea monster Leviathan is scattered throughout the Bible, and like the manna of Leviathan's shattered head (Psalm 74:14), it nourishes and enriches the text.
When the LORD utters the words, "Be still," the whole earth melts. The melting process involves dissolving the boundaries between things so that they merge together. Ice cubes are rigidly bound individual pieces of water, but when they melt they lose their defined shapes and descend into formlessness, merging together into a puddle and making it impossible to know where one cube ended and another began. When we hear God's voice ("Be still"), things melt away to reveal the unity behind apparent multiplicity. God's voice dissolves boundaries.
However, God also creates boundaries. In the next verses, the psalm speaks of "a river whose streams make glad the city of God." The city image is one of a complex organization opposed to nature, while the river is the flowing, boundless water of chaos-nature organized into a directional pattern, bounded on either side by banks. It is an image of organized chaos, of organized innocence. The total image is one of high systemization nourished (and made glad) by the living waters of organized innocence. As I conceive it, the city is surrounded by walls, boundaries that separate and strengthen it. The river rushes through the gates and around the gardens within, providing life, growth, and change. At the center of the city of God, in the holy-of-holies, is the LORD himself ("God is in the midst of her"), an internal creative fire. Essentially it is a wild chaos of water outside and an untamed flame within, surrounded and separated by the walls of restraint. It is a cartography of the divine man utilizing the subterranean wonder of messy life and the endless expanses of the heavens--bounded, vivified, and holy. God shows us the essential unity behind the many facades of life, then shows us how to draw from this boundless unity and drink from the waters of Life.
*By the way, to anyone who cares, the phrase "It's melting time," comes from Ibsen's Peer Gynt, where the wryly grim Button Moulder threatens Peer with identity-dissolution.