SWAMI VENKATESANANDA explains the concept of pure consciousness in his commentary on the YOGA VASISHTA

Shiva spoke thus: Consciousness thinks falsely ‘I am happy’. Just as one who is not dead wails aloud ‘Alas, I am dead’, because of perverse understanding, even so consciousness falsely imagines it is miserable and limited. Such imagination is irrational and unfounded. Due to the false assumption of ego sense, consciousness thinks that the world appearance is indeed real. It is the mind alone that is the root cause of experiencing the world as if it were real; but it cannot be truly considered such a cause since
there can be no mind other than pure consciousness. Once you realise that the perceiving mind itself is unreal, it becomes clear that the perceived world is unreal, too.

Even as there is no oil in a rock, in pure consciousness the diversity of sight, seer and scene, or of doer, act and action of knower, knowledge and known does not exist. Similarly, the distinction between ‘i’, and ‘you’ is imaginary. The distinction between the one and the many is verbal. All these do not exist at all even as darkness does not exist in the sun. Opposites like substantially and insubstantiality, void and nonvoid are mere concepts. On enquiry, all these disappear and only unmodified pure consciousness remains.

Significance Of Self-effort
Consciousness does not truly undergo any modification nor does it become impure. The impurity itself is imaginary; imagination is the impurity. When this is realised, the imagination is abandoned and impurity ceases. However, even in those who have realised this, the impurity arises unless the imagination is firmly rejected. By self-effort, this imagination can be easily rejected: if one can drop a piece of straw, one can with equal ease also drop the three worlds! What is it that cannot be achieved by one’s self- effort?

This infinite consciousness, which is unmodified and non-dual, can be realised by one in the single self-luminous inner light. It is pure and eternal, it is ever present and devoid of mind, it is unmodified and untainted, it is all the objects. In fact, it is nonmoving consciousness which exists as if witness to all, even as light shines but shining is not its action. While pure, this consciousness appears to be tainted; in inert material, it is non-inert energy. It is omnipresent without being divided by the particulars constituting them all.

This infinite consciousness, which is devoid of concepts and extremely subtle, knows itself. In self-forgetfulness, this consciousness entertains thoughts and experiences perceptions, though all this is possible because of the very nature of the infinite, consciousness, even as one who is asleep is also inwardly awake.

Pure Consciousness
By identification with its own object, consciousness seems to reduce itself to the state of thinking or worrying, even as impure gold looks like copper until it is purified, when it shines like gold. By self-forgetfulness on the part of the infinite consciousness, the notion of the universe arises, but this unreality ceases with self-knowledge.

When consciousness becomes aware of itself within itself, the ego sense arises. With just a little movement though, this ego sense falls down as a rock rolls down the mountainside. However, even then it is consciousness alone that is the reality in all forms and all experiences. The movement of the vital air brings about vision within and an object which is apparently outside. But the experiencing of sight is the pure consciousness. The apparently inert vital air which is the tactile sensation comes into contact
with its object and there is the sense of touch. But the awareness of the tactile sensation is again pure consciousness. In the same way, it is the vital air that enables the nose to smell the scents which are modifications of the same energy, while the awareness of the smell is pure consciousness. If the mind is not associated with the sense of hearing, no hearing is possible. Again, it is pure consciousness that is the experience of hearing.

Action springs from thought, thought is the function of the mind, mind is conditioned consciousness, but consciousness is unconditioned. The universe is but a reflection in consciousness but consciousness is not
conditioned by such reflection. Jiva is the vehicle of consciousness, ego sense is the vehicle of jiva, intelligence of ego sense, mind of intelligence, prana of the mind; the sense of motion is karma. Because prana is the vehicle for the mind, where the prana takes it, the mind goes. But when the mind is merged in the spiritual heart, prana does not move. And if the prana does not move, the mind attains a quiescent state. Where the prana goes, the mind follows, even as the rider goes where the vehicle goes.

Only One Reality
The reflection of consciousness within itself is known as puryastaka. Mind alone is puryastaka, though others have described it more elaborately (as composed of the five elements, the inner instrument — mind, buddhi, ego sense and chitta — prana, the organs of action, the senses, ignorance, desire, and karma or action). It is also known as the linga-sarira, the subtle body. Since all these arise in consciousness, exist in consciousness and dissolve in consciousness, that consciousness alone is the reality.

But for the mind and prana, the body is an inert mass. Just as a piece of iron moves in the presence of a magnet, even so the jiva moves in the very presence of consciousness that is infinite and omnipresent. The body is inert and dependant; it is made to function by the consciousness which believes itself to be similar to the prana or vital air. Thus, it is the karmatama, karma-self or the active self, that keeps the body in motion. It is, however, the Supreme Self itself that has ordained both the mind and the prana as the promoters of life in the body. It is the consciousness itself, assuming inertia, which rides the mind as the jiva.

The Supreme Yoga: Yoga Vasishta, MLBD