One of the greatest contributions of India is the metaphysics of self knowledge called Samkhya, which says the knowledge of an object, the object itself and the process of knowing is all one. This is the essence of wisdom and experientially accessible for anyone through the practice of Yoga. Yoga thus is the methodology to test this hypothesis of samkhya, just like we do the lab experiment to prove a theorem in modern physical sciences.
There is no single English word to convey the meaning of the Sanskrit word prana, the nearest word in English is probably "life energy" or "vital energy" that permeates the whole universe and our bodies. The breath that goes in and out of our bodies connect the microcosm within to the macrocosm and if one breath that goes out does not come back life is finished, isn’t it? Prana is in a way our real Mother in whom we are born, sustained and to whom we go back to. The inhalation is the inspiration for life itself and exhalation is the main expiration of toxins from our biological system that keeps us alive and conscious. Breath, like a power plug acts as the source of our entire energy supply to every cell.