Maya or illusion is the most important contribution of Sage Sankara.+

Maya or illusion is the most important contribution of Sage Sankara. Maya or illusion is the complex illusionary power of the Atman (Soul), which is present in the form of consciousness. 

Consciousness is the ultimate reality or Brahman, and Ignorance is the cause of experiencing the duality as a reality.

Maya or illusion is present in the form of the mind. And the mind is in the form of the universe. And universe appears as a waking or dream (duality) and disappears as deep sleep (Nonduality).

The waking experience is real from the standpoint of the waking entity (ego). Waking experience is unreal from the standpoint of the   Soul, the ‘Self’.  

The cause of the three states is consciousness (consciousness itself’ is untouched by the profanity of illusion (Maya). Illusion (Maya) is temporary and is destroyed with Self-knowledge or Brahma Gnana or Atma Gnana.”

Rig Veda: ~ 'Prajnanam Brahma'- Consciousness is the ultimate reality or Brahman or God in truth.

Do not accept any other truth other than consciousness. Consciousness is the ultimate truth,  Nothing is real but consciousness. Nothing Matters but to realize the ultimate truth. Consciousness is everywhere and in everything. Let these words be inscribed in your subconscious. 

Bhagavad Gita: ~ Brahman is considered the all-pervading consciousness, which is the basis of all the animate and inanimate entities and material. rahmano hi pratisthaham, Bhagavad Gita 14.27)

If Brahman is considered the all-pervading consciousness then, it is necessary to realize, the consciousness as the ‘Self’, which pervades all the three states, to realize the fact that there is no second thing exists other the consciousness. Thus, consciousness (Atman) is the ultimate truth (Brahman).  

Sage Sankara’s notion of Maya, the cosmic illusion, which must be transcended in order to realize the truth of Brahman, which means the ultimate truth.  

Sage Sankara: ~ VC:~  "As layers of clouds generated by the sun's rays cover the sun and alone appear (in the sky), so egoism generated by the Self, covers the reality of the Self and appears by itself."

Sage Sankara: ~ VC~ "All this universe which through ignorance appears as of diverse forms, is nothing else but Brahman which is absolutely free from all the limitations of human thought.

Sage Sankara said:~  Just as the snake is superimposed on the rope in the twilight, this world and body are superimposed on Brahman or the Supreme ‘Self’. If you get knowledge of the rope, the illusion of a snake in the rope will vanish. Even so, if you get knowledge of Brahman or the Imperishable, the illusion of body and world will disappear.  The cause produces the effect without undergoing any change in itself’. Snake is only an appearance on the rope. The rope has not transformed itself into a snake, like milk into curd. Brahman is immutable and eternal. Therefore, It cannot change itself into the world. Brahman becomes the cause of the world through Maya, which is its inscrutable mysterious power. When you come to know that it is only a rope, your fear disappears. You do not run away from it. Even so, when you realize the eternal immutable Brahman, you are not affected by the phenomena or the names and forms of this world. When Avidya or the veil of ignorance is destroyed through knowledge of the Eternal, when Mithya Jnana or false knowledge is removed by real knowledge of the Imperishable or the living Reality, you shine in your true, pristine, divine splendor and glory

Only in ignorance, the world in which we exist is an illusion created out of the Soul, the ‘Self’. 

The world is both real and unreal. It is real because it is a manifestation of consciousness, but is unreal, in the sense, that it is not absolute and eternal like consciousness itself.

People's approach is more practical, and they stuck with the reality of the world, they take it as real. That is why all the confusion. 

The look of an object will depend upon the medium through which the observer views it. In fact, our mental and intellectual conditions determine the world, observed and experienced. The commoner viewing the world will see differently from a Gnani viewing the same world. Each one interprets the world that they see in terms of their existing knowledge. The commoner sees everything based on the ego, therefore, experiences the birth, life, death and the world as a reality, whereas a Gnani sees everything as consciousness and he is fully aware of the fact that, there is no second thing that exists other than the Soul or consciousness. 

Thus, all the egocentric (religious) adulteration has to be bifurcated to realize the ultimate truth, which is beyond form, time and space. : ~ Santthosh Kumaar