The aim behind all the hatha yoga postures is to be able to sit in one steady, comfortable position for meditation. It is only in a steady posture that you can have a good meditation. A body filled with toxins, weak muscles and jumpy nerves will not be able to stay quiet for any length of time. But the hatha yoga postures eliminate the toxins and give strength and steadiness. When the body is healthy and supple, you can easily sit with the mind still and peaceful. As you begin to control the body and its movements, that control will carry over to the mind.
Try this yourself. Any time the mind is agitated, just sit quietly, not moving at all. Let the mind be as agitated as it wants. If your body is still, very soon the mind will calm down all by itself. Why? Because when there is no physical movement, the breath becomes slow; and the breath is the interconnection between mind and body. As the breath slows, the thought-making process slows down and the mind becomes calm.
The asanas or postures help to train the mind. Without purity of body, it is very difficult to purify the mind. Learn to live a natural life. First be physically at ease, and mental peace will follow. Live in a way that makes your body light, healthy and more supple. Then when you sit for meditation, you won't feel aches and pains and spend your time meditating on them.
Om Shanthi, Shanthi, Shanthi