How does the imagery of (i) the fish (ii) the tree, used almost poetically by the author, emphasising the idea of stillness of living, breathing thought?

The narrator contemplates the life a tree and a fish to emphasize upon the idea of stillness of living, breathing thought. She says “Wood is a pleasant thing to think about. It comes from a tree, and trees grow, and we don’t know how they grow” to describe how the still nature works silently without paying attention to the world around. Then she further explains it using the imagery of a fish saying, “I like to think of the fish balanced against the stream like flags blown out” to describe the still life that is present in a parallel world around us that is often left unseen. Everything around us is moving, falling, slipping and vanishing or as the narrator says, “There is a vast upheaval of matter”.