Atman is the ultimate truth and Atman is formless and non-dual in its nature.

Atman or the soul or consciousness or self are one and the same thing. Atman is the ultimate truth and Atman is formless and non-dual in its nature. Atman  is falsely conceived as taking part in birth and death, coming and going and as existing in all bodies; but howsoever it be conceived, it is all the while not different from its true nature .

 All things that appear as compounded are but dreams and illusion. Duality is a distinction imposed upon the Atman by illusion. The Atman is immortal; it cannot therefore by its own nature suffer change. It has no birth. All birth and death, this entire manifold is but the result of an imposition of illusion upon it.

Atman appears as many in the dream, so also in the waking experience, the Atman appears as many, but when the mind is stilled then arises, the non-dual natural state free from fear, and all sorrows, final cessation.

Thinking experience of duality to be misery one should divert his attention from desires and enjoyments and thinking always of the Atman as true self. In this way he should awaken the mind into its final dissolution and pacify it when distracted, he should not move it towards diverse objects when it stops.

The seeker should constantly reflect on Atman and by wisdom remain unattached, by strong mental effort making it motionless and still, when he neither passes into dissolution nor into distraction; when there is no sign, no appearance that is the perfect state of Atman. When there is no objective awareness it is the formless non-dual state of Atman. That is the nature of Sahaja Samadhi. 

YOGA VASISHTA:-

The mind, the intellect, the senses, etc. are all the play of Consciousness. They are unreal and seem to exist only due to lack of insight.

I, the pure, stainless and infinite Consciousness beyond Maya, look upon this body in action like the body of another.

If one realizes the unity of things everywhere, one always remains tranquil, inwardly cool and pure like space without the sense of 'I'.

Just as the whole tree with all its future ramifications is in the seed, the entire universe of the past, the present and the future is contained in the atom of infinite consciousness.

Therefore, though the self is neither the doer of actions nor the experiencer of experiences, it is the doer of all actions and the experiencer of all experiences: there is nothing apart from it.

Within the atom of infinite consciousness the doership and the experiencer are inherent.

The world, however, has never really been created, nor does it disappear: it is regarded as unreal only from the relative point of view, from the absolute point of view it is non-different from the infinite consciousness.

Consciousness (soul) is the substance and witness of the duality.  The duality is present in the form of mind. Mind is present in the form of universe. The universe appears as waking or dream and diapers as deep sleep. The one which is aware of the coming and going of the three states is neither the waking entity nor the dream entity but the formless soul, which is present in the form of consciousness.  When the soul becomes aware of its formless nondual true nature in the midst of duality it is called self –awareness. It is foolish to limit the consciousness only to duality because the consciousness pervades all the three states