Asana is dynamic and active even though the body appears still. Each pose contains a multitude of actions – extensions, contractions, lateral movements, vertical movements, and circumferential movements. Each of those actions is balanced by an opposing action. In Virabhadrasana (Warrior) II, for instance, the action of the right knee bending is opposed by the action of the left thigh lifting. The right arm extending forward is opposed by the left arm extending backward. The lift of the spine is opposed by the feet extending into the earth. As those forces balance, the body is still but not static. It is vibrant.
Initially, the mind treats each part of an opposing pair as separate. The left thigh lifts, the right knee bends. Gradually, a sense develops that the thigh lifting and the knee bending are parts of the same action of opening. The mind integrates the two opposing actions and that integration becomes something more than its parts. The opening becomes the focus. That opening integrates with other openings, like the balance between the right knee and left thigh both moving from front to back. Both of those openings merge into a single action which incorporates the two original pairs of opposing actions.
Each action can also be broken down into component pairs of actions. In Virabhadrasana II, on the bent knee leg, the head of the femur drops as the hip bone lifts. On the straight leg, the external rotation of the leg balances with the depth of the groin. The awareness can break down a pose in an almost fractal way into component balancing pairs.
The practice is to penetrate a pose into its component parts even as those parts are integrated into a single whole. Over time, you learn to balance these two opposing processes.
There is also the practice of creating balance between the right and left side of the body. The lessons learned doing Virabhadrasana II with the right knee bent may be different than those learned doing the pose with the left knee bent. An action that is easier when you do the pose on one side can teach you how to do that action on the other side where it is more difficult. And when that action is learned on the more difficult side, there will be a depth of understanding that will be able to teach the easier side.
Over time, as you learn to balance the left and right side of the body, you create equal strength and flexibility between the left and right arm, left and right leg, left and right side of the trunk. Our asymmetries pull the spine out of alignment, which distracts conscious awareness and makes it more difficult to access core energetic and emotional strength. When the functional core of our structure is held by the muscles or organs rather than by the spine, there is a greater tendency to seek identity outside of ourselves and a large amount of vitality is consumed by maintaining that false core.
The chronic gripping that maintains an unbalanced body makes it much more difficult to access that sense of spaciousness or peacefulness inside. The balance learned through asana not only can remove impediments to that inner peace, but the discrimination and integration learned on the physical level teach you how to approach the deeper levels of yourself.