6 ideas
The mind-stuff (chitta) is a material substance that takes the shape of whatever it perceives, forming waves or modifications (vrittis), just as still water takes the shape of an object thrown into it. Yoga is defined as the deliberate restraint of these modifications, so the underlying substance can return to stillness and reflect its true nature.
Suffering arises because the pure witnessing Self identifies itself with the agitated mind, mistaking the colored, moving reflection for its own nature. When the mind-waves are stilled, the Self rests in its own unchanging form rather than borrowing identity from passing mental states.
Liberation is approached through eight sequential limbs: restraint (yama), observance (niyama), posture (asana), breath control (pranayama), withdrawal of senses (pratyahara), concentration (dharana), meditation (dhyana), and absorption (samadhi). The earlier limbs prepare body and ethics so the later, purely mental disciplines become possible — each stage is a precondition for the next.
Behind physical breathing lies prana, the subtle energy animating all motion in the body and universe; the breath is merely the flywheel that lets you reach and control this finer force. By rhythmically regulating inhalation, retention, and exhalation, one gains command over the nerve-currents and ultimately over the mind itself.
Every thought and action leaves an impression (samskara) sunk into the mind-substance, and the sum of these residues forms character and drives future tendencies without conscious awareness. Habits and personality are therefore not fixed but are accumulated deposits that can be overwritten by deliberately laying down opposite impressions.
All knowledge — scientific, artistic, or spiritual — is produced by concentrating the scattered powers of the mind onto a single object, and the difference between an ordinary and an extraordinary mind is degree of concentration. Yoga systematizes this faculty so it can be directed inward, making the mind both the instrument and the object of investigation.