Psalm 23 is full of rich metaphor and imagery. In verse 2 speaking of God as his shepherd David says that He led him beside still waters.
Still waters speak to me of a state of peace. In still water you see a reflection. A reflection of reality, a tree or a mountain, whatever happens to be beside the water.
When we allow God to lead us by still waters, to calm and bring peace to our internal world, it is in that state we see a reflection of reality, the reality of heaven, of life as God sees and defines it, as oppose to the tattered version of life we see when viewed and defined through our harried, restless souls.
Allow God to lead you by still waters, so you see and live out of a reflection of heaven in your soul.