Everything is subject to change. In the photograph above the stones on the beach have been gradually broken down into smaller pieces, and this will continue until they are pebbles and then merely small grains of sand on the shore.
This grinding down could also have been illustrated with millstones, which reduce grain into a smaller and finer substance. Often this has been used as a metaphor for our spiritual life, where the gradual daily grind of physical life produces a finer and ‘higher’ spirituality.
However, the best way to achieve spiritual change is to transform our thinking. Constant reappraisal of our thoughts and beliefs will gradually make a transformation not only of our minds but our actions as well.