Excerpt from a talk given by Shinzen Young called Understanding Impermanence:
The word for spirit in English is from the Latin, spīritus which is a translation of a Greek word, pneuma. Pneuma is a translation of a Hebrew word, ruach which means breath or wind. So when we say we’re on a spiritual path, people can interpret this in a lot of different ways. I like to interpret it literally. You are on a path to becoming spiritualis. You are on a path to becoming wind-like: powerful and insubstantial and unfixated.
The native people of the plains of North America have a natural way of expressing this idea. In the Sundance ceremony, you dance around a cottonwood tree. If you look at a cottonwood tree, it’s a little different from other trees. It has the ability to respond to the wind very immediately. With the tiniest little movement of wind, you can see the direction and magnitude of the wind at a very fine scale in the accelerations and decelerations of each little leaf in the cottonwood tree. You can see ruach in that tree. So you dance around that tree and look at that tree for four days. It gets you in sync with one of the flows of nature.
And why does that tree work that way? Well, if you look at the way the leaves are articulated on the stems, they are very pliant instead of being rigid. There’s a link between our equanimity, a kind of pliancy in our sense gates, so that the more equanamous we become, the more we literally vibrate with ruach, with spirit, with the wind, with the basic forces of nature.