“Prana is the universal principle of energy or force. It is vital force. It is all-pervading. It may be either in a static or a dynamic state. Prana is force on every plane of being, from the highest to the lowest. Whatever moves or works or has life, is but an expression or manifestation of Prana.
Prana is the sum total of all energy that is manifest in the universe. It is the sum total of all the forces in nature. It is the sum total of all latent forces and powers which are hidden in men and which lie everywhere around us. Heat, light, electricity, magnetism are the manifestations of Prana. All forces, all powers and Prana spring from the fountain or common source, ‘Atman’. All physical forces, all mental forces come under the category ‘Prana’.
The Prana is related to mind and through mind to will, and through will to the individual soul, and through this to the Supreme Being. If you know how to control the little waves of Prana working through the mind, then the secret of subjugating universal Prana will be known to you. The Yogi who becomes an expert in the knowledge of this secret, will have no fear from any power, because he has mastery over all the manifestations of powers in the universe. What is commonly known as power of personality is nothing more than the natural capacity of a person to wield his Prana. Some persons are more successful in life, more influential and fascinating than others. It is all due to the power of this Prana.
It is Prana that shines in your eyes. It is through the power of Prana the ears hear, the eyes see, the skin feels, the tongue tastes, the nose smells, the brain and the intellect do their functions.
Prana is electron. Prana is force. Prana is magnetism. Prana is electricity. It is Prana that pumps the blood from the heart into the arteries or blood vessels. It is prana that does digestion, excretion and secretion.
Prana is the link between the astral and physical body. When the slender thread-link Prana is cut off, the astral body separates from the physical body. Death takes place. The Prana that was working in the physical body is withdrawn into the astral body.
Breath is the external manifestation of Prana, the vital force. Breath is gross. Prana is subtle. By exercising control over the gross breath, you can control the subtle Prana inside.”
Swami Sivananda
Bliss Divine, Page 376 and Divine Life Society website