3 ideas
The mind-stuff (chitta) is a calm lake whose surface gets disturbed into waves (vrittis) by external impressions and internal reactions. Yoga is defined precisely as restraining these waves so the agitated mind settles, allowing the true Self to be reflected undistorted rather than seeming to take the shape of each passing thought.
Mastery progresses through eight sequential stages: ethical restraints (yama), observances (niyama), posture (asana), breath control (pranayama), withdrawal of senses (pratyahara), concentration (dharana), meditation (dhyana), and absorption (samadhi). Each lower limb stabilizes the body and nerves enough to make the next inner stage possible, so concentration is reached by physical and moral preparation rather than by direct force of will.
Every form of knowledge — practical, scientific, or spiritual — is produced by the power to gather and hold the mind on a single point. The difference between an ordinary mind and a genius is not a different faculty but a greater capacity for sustained concentration, which can be deliberately trained like a muscle.