Sheer joy! The image is of a carefree young girl singing to herself while engaged in her work. Happiness rising within, and spreading out into the world!
Joy comes into the world through gentle means, but springs from a solid inner base. The power of great joy should not be underestimated. The sheer joy of learning and discovery, for example, has been the source of much material progress. Accordingly, that which brings joy into the world is a source of considerable power.
