They describe a way of being in harmony with the nature of all things. Born of my body, mouth, and thought. Body, mouth, and thought are the spheres of action where karma is created, both good and evil. What we do with our bodies, what we do with our words, and what we do with our thoughts, all lead to consequences, all establish specific karma. We should appreciate this fact thoroughly.
Body language speaks outwardly and inwardly.
When you clench your fists and grit your teeth, you create anger mentally and physically. When you place your hands in the cosmic mudra, you create a state of consciousness that reflects introspection and peace. What we do with our bodies is who we are. It is for that reason that the posture of zazen is so important. When we bow, we manifest the body karma of the three virtues.