"Vāyu, the subtle power of the breath, is the very epitome of God. In fact, vāyu is God himself. So, when a person breathes, God is at work. As you know, without the power of the breath, a human body will die. The śāstras recognize this vital fact of life, and accord it all the importance that it deserves. The reason that proper breathing is vital to the practice of yoga is that it enables you to calm your mind, and allows good thoughts to filter in. Without it, disorientation of the mind will occur and breathing patterns will become seriously affected. The whole basis of proper breathing is to insure a perfect state of mind, that is, a mind that is not agitated, angry and unstable. The Bhagavad Gitā, which is all encompassing, explains the importance of uniform breathing, as I said earlier. So, if you inhale for ten seconds, for example, you should also exhale for the same length of time. This will insure the maintenance of the body's equilibrium. Before we conclude, though, I would like to stress again that yoga is for everyone - man, woman, the young, old, healthy, infirm. It is all a matter of having an inclination for it. Laziness or lack of interest are the only things that get in the way of its practice, nothing else. That is a universal truth."
(Sri K. Pattabhi Jois, Sūryanamaskāra)