‘Benefits of breath control’ is from the Complete Works of Swami Vivekananda, (Kolkata: Advaita Ashrama, 2016), 1.490-92.
We see with our common sense that it is the breath that is setting everything in motion. If I stop breathing, I stop. If the breath begins, the body begins to move. What we want to get at is not the breath itself. By the help of things on the material plane, we have come to finer and finer perceptions.
The universe is one, whatever point you touch. All the points are but variations of that one point. Throughout the universe is a unity at bottom. Even through such a gross thing as breath I can get hold of the Spirit itself. By the exercise of breathing we begin to feel all the movements of the body that we now do not feel. As soon as we begin to feel them, we begin to master them. Thoughts in the germ will open to us, and we will be able to get hold of them. Of course, not all of us have the opportunity nor the will nor the patience nor the faith to pursue such a thing; but there is the common sense idea that is of some benefit to everyone.
The first benefit is health. Ninety-nine percent of us do not at all breathe properly. We do not inflate the lungs enough. Regularity of breath will purify the body. It quiets the mind. When you are peaceful, your breath is going on peacefully, it is rhythmic. If the breath is rhythmic, you must be peaceful. When the mind is disturbed, the breath is broken. If you can bring the breath into rhythm forcibly by practice, why can you not become peaceful? When you are disturbed, go into the room and close the door. Do not try to control the mind, but go on with such rhythmic breathing for ten minutes. The heart will become peaceful. These are common sense benefits that come to everyone.
Deep-breathing exercises are only the first step. Some people have taken up this breathing as the whole pursuit of life. They do not do anything without consulting the breath. They are all the time observing in which nostril there is more breath. When it is the right, they will do certain things, and when it is the left, they do other things. When the breath is flowing equally through both nostrils, they will worship. When the breath is coming rhythmically through both nostrils, that is the time to control your mind.
By means of the breath you can make the currents of the body move through any part of the body, just at will. Whenever any part of the body is ill, send the Prana to that part, all by the breath.