“He who knows Prana knows Vedas” is the important declaration of the Srutis. You will find in Vedanta Sutras: “For the same reason, breath is Brahman.” 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’. It 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. Akasa or ether also is an expression of 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.
From The Science of Pranayama by Sri Swami Sivananda