Therefore the mystics keep all the passages of the breath open. They fast. They practice abstinence. The proof of the heart, the soul, is in the breath. When we are very sad a deep sigh comes, a very heavy sigh. This shows that the breath has come in contact with something that has made it heavy, that is the heart: not this heart of flesh, but the inner heart. The life exists in the breath. When the breath is gone, the mechanism of the eyes is perfect, but we do not see. The mechanism of the ears is perfect, but we do not hear. The essence is in the breath. If we can see and hear by the physical organs, why should we not see and hear much more by the breath, since the essence is there?