If the present the world in which you exist is mere an illusion, then whatever you believed as a real in this world in which you exist is bound to be an illusion.+

When ‘Self’ is not ‘you’ then whatever you have seen, known believed, and experienced as reality is bound to be an illusion. Thus, self-realization is necessary to realize your present the world in which you exist is merely an illusion. 

If the present world in which you exist is merely an illusion, then whatever you believed as real in this world in which you exist is bound to be an illusion.

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

When Bhagavad Gita says, God is considered the all-pervading consciousness which is the basis of all the animate and inanimate entities and material then nothing has to be accepted as God other than consciousness. 

Religious Gods are not God in truth. One must realize  God in truth.

Lord Krishna says Ch ~V: ~ “Those who know the Self in truth.". The last two words (tattvataha) are usually ignored by pundits, but they make all the difference between the ordinary concept of God and the truth about God. 

The dualistic worship of "God” is only for the ignorant populace. The God in truth is only Atman, the innermost ‘Self’. In reality, there is no duality, no differentiation. Only Atman exists. 

From the dualistic perspective, people see the world in which they exist as a reality.    They see their body as the body, their ego as the ego, and the world in which they exist as the world whereas a Gnani sees everything from the nondualistic perspective.  

A Gnani sees his body as consciousness, his ego as consciousness, and the world in which he exists as consciousness.  For a Gnani, whatever is seen, known, believed, and experienced is nothing but consciousness.  There is unity in diversity in Gnani's understanding whereas the ignorant people see only diversity and separation.

Thus, it is necessary to learn to view and judge the worldview from the non-dualistic perspective in order to realize that form, time and space are one in essence. There is nothing to realize other than realizing that consciousness is everything. Consciousness is second to none.  

When everything is nothing but consciousness then what remains which is not  consciousness

The world in which we exist 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.

That is why Sage Sankara says: ~  VC-63. Without causing the objective universe to vanish and without knowing the truth of the ‘Self’, how is one to achieve liberation by the mere utterance of the word Brahman? — It would result merely in an effort of speech. :~Santthosh Kumaar