Depending on what tradition of yoga you follow, Physical Postures (Asanas) are the 1st or the 3rd limb. Either way, they are of fundamental importance.
Physical Postures play 3 significant but different roles in the practice of yoga: 1) physical health, 2) energetic flow and 3) a seat for meditation.
The first purpose is physical health. This is the most common use of yoga postures. When the body is weak or ill, it is impossible for us to be content, happy or to make spiritual progress. If we want to be happy, we must first be healthy, so physical illness is the first obstacle we must overcome. In order to eradicate bodily illness and perfect bodily function, yogic physical practice is designed to heal each part of the body and make it strong. That is why it is such an effective form of what we might call "physical fitness." While many other forms of physical fitness, like running, lifting weights or swimming, focus on the muscular and cardiovascular systems, either ignoring or sacrificing other bodily systems like the joints, organs, circulatory, endocrine and nervous systems, yogic physical practice (ideally) exercises every inch of the body inside and out. This is the founding principle of Ghosh Yoga, the style that I practice most ardently.
Once the physical body is healthy and strong, the energetic body comes to life. The second purpose of Physical Postures is focusing and freeing the energetic flow. Like Tai Chi and QiGong, yoga postures create open pathways for the powerful energy that flows through the body. Usually this energy lies dormant because our stress inhibits it or our body is too weak to handle it. With yoga postures, we can awaken that energy and focus it. This leads to radiant physical health and emotional and intellectual insight and intuition.
The third and most ancient reason for yoga postures is meditation. When we meditate, we must sit still for long periods of time, and unless we are strong enough and aligned properly it is quite difficult. There are several postures in yoga designed specifically for sitting in stillness or preparing us to sit in stillness. These postures encourage good spinal alignment that draws our energy up the spine.
This journal honors my ongoing experience with the practice, study and teaching of yoga.
1) Sridaiva Yoga: Good Intention But Imbalanced
2) Understanding Chair Posture
2) Why I Don't Use Sanskrit or Say Namaste
3) The Meaningless Drudgery of Physical Yoga
5) Beyond Bikram: Why This Is a Great Time For Ghosh Yoga