In the book Yoga Vasistha, Sage Vasistha gives answers to questions of Lord Rama. One question and answer explains us the importance of Pranayama in yoga and its vital importance in mastering the power of Kundalini.
A excerpt from Yoga Vasistha..
Ram again said to the Master: "Please explain how mental disease can be destroyed."
The Master answered: "Diseases which affect the mind are the first and are not the easiest to heal; those which affect the body may be classed as secondary. The desires which affect the mind are primary diseases; we have sunk thus far by absence of Wisdom, and lack of Mastery over ourselves. We are under the seeming power of delusion. We cannot realise to what extent we arc pulled down by such delusion. The mental disease is similar to the coming of a winter storm. When the power of desires gets hold of one, he then is liable to be guilty of fearful karma (wrong action); this in turn produces bodily disease.
"Bodily disease is also brought on by overeating, living in unhealthy places, association with the wicked, impure desires, evil thoughts, etc. These mental or indirect diseases have a direct effect upon the body.
"Now I will explain how both forms of disease perish, O Ram. The wise say that the mental diseases have two divisions, common and specific, the former affect this body only, but the latter tend to rebirth, also. The common diseases may be banished by correct eating and right thinking.
"When the mind is not in perfect harmony it may affect the blood and produce discord in any portion of the body. Mental discord will produce poison in the blood, and the poison will affect the nervous system. When the nervous system is affected, then Prana (Vital Force) cannot follow its right path. When Prana does not follow its right path, then it cannot reach all parts of the body as it should, and thus many of the nerves may wither or die. If harmony is established in the mind, all else is easy and simple. When harmony is established in the mind, it will naturally follow, that one will want to do good and read good books pertaining to truth. When peace is established in the mind, then Prana will follow its right course and all disease will vanish.
"The path of Yoga, by which one may master the power of the Kundalini, is through the practise of Pranayama, which causes the power of the Kundalini to arise, and then the holy becomes strong. By Pranayama the movement of Prana and Apana may be controlled; then the Yogin will be able to go up like a bird. The Prana is the cause, and when it is made to go up through the Sushumna, all kinds of psychic powers are attained, such as seeing, hearing and levitation."