Raja Yoga remains something of a mystery for most people who have an active outer life, because it requires extensive practice and discipline to achieve total stillness in the body and a cessation of the waves of mental energy in the mind. When practiced seriously it can be a tool of tremendous power to both enhance the mental force, achieving thereby powers of concentration and other occult results, and achieve a divine union, liberating the practitioner from the subjection to the outer life and the mind’s attachment to the objects of the senses.
Sri Aurobindo describes the science of Raja Yoga briefly: “Our ordinary mentality is first disciplined, purified and directed towards the divine Being, then by a summary process of Asana and Pranayama the physical force of our being is stilled and concentrated, the life-force released into a rhythmic movement capable of cessation and concentrated into a higher power of its upward action, the mind, supported and strengthened by this greater action and concentration of the body and life upon which it rests, is purified of all its unrest and emotion and its habitual thought-waves, liberated from distraction and dispersion, given its highest force of concentration, gathered up into a trance of absorption. Two objects, the one temporal, the other eternal, are gained by this discipline. Mind-power develops in another concentrated action abnormal capacities of knowledge, effective will, deep light of reception, powerful light of thought-radiation which are altogether beyond the narrow range of our normal mentality; it arrives at the Yogic or occult powers around which there has been woven so much quite dispensable and yet perhaps salutary mystery. But the one final end and the one all-important gain is that the mind, stilled and cast into a concentrated trance, can lose itself in the divine consciousness and the soul be made free to unite with the divine Being.”
Sri Aurobindo, The Synthesis of Yoga, Part Four: The Yoga of Self-Perfection, Chapter 1, The Principle of the Integral Yoga, pp. 583-584