The fourth sheath of your whole body is said to be composed of “deep understanding”. The mind (mano-maya kosha) simply coordinates the sensory input and the motor output… but understanding is a higher function.
“Separate from that self comprised of mind, there is another internal self constituted by intelligence…of this self, faith is her head, righteousness is her right wing, truth is her left wing and yoga is her trunk” Taittiriya Upanishad
Vijnana-maya kosha allows us greater perspective and insight, better discrimination and sensible detachment. It imparts healthy conscience, common sense and has a very “humane human” quality compared with the first three sheaths.
Early yogis considered the development of a healthy Vijnana-maya kosha so important that they placed the practices for it before physical poses at the very beginning of the yoga system. These are the yamas and niyamas, a code of ethics urging us not to harm, lie, steal, binge, or grasp for more than we need. Instead we are asked to try to practice cleanliness, contentment, self-discipline, continuous self-study, and devotion.
Regular meditators become aware of Vijnana-maya kosha as they start to identify those regular patterns of the mind as just that: entrenched patterns and habits composed of thoughts. Then a deeper realisation and understanding seems to settle and a dependable relationship with inner guidance develops. Once-disturbing thoughts now lose their charge and clarity and a way ahead becomes apparent.