In this book the factor of mind in meeting present-day needs is given prominence as the agent of the soul, and the key to personality release. These Yoga Sutras of Patanjali are based on Raja Yoga, the "kingly science of the soul": "Through the science of Raja Yoga the mind will be known as the instrument of the soul and the means whereby the brain of the aspirant becomes illuminated and knowledge gained of those matters which concern the realm of the soul." Patanjali explores exhaustively the means, the techniques and the mental posture which create the connecting thread between the form-centred personality and these stages towards spiritual achievement and soul fusion. The four parts of the book develop: I. The Problem of Union (51 sutras). 2. The Steps to Union (55 sutras). 3. Union Achieved and Its Results (55 sutras). 4. Illumination (34 sutras). Sutra 31 of Part IV rings out like a bell and a clarion call to those who venture on the path of union with the soul. "When through the removal of hindrances and the purification of the sheaths, the totality of knowledge becomes available, naught further remains for the man to do."