AUM represents the three states and everything that exists. True knowledge has only one consequence of making one firmly believe in the unreality of this world, if you know them.
It only teaches the unreality but does not destroy. If a true knowledge of the Self were able to destroy the entire world, then it would also put an end to the fructification of past deeds. But it only teaches the unreality and does not destroy it.
If you say you get Gnana in Nirvikalpa Samadhi, and then why not admit it in deep sleep?
Sage Sri, Goudpada expands further on these states of consciousness. The Self is AUM. It represents manifest and un-manifest aspects of Brahman. It is the single syllable that symbolizes and embodies Brahman, the Absolute Reality. It is the Pranava that which pervades all existence and is our very life breath.
Vaisvanara in waking the state is A the first part of AUM, One, who realizes this, attains his desires.
Teijasa in dream state is U the second part of AUM. One, who realizes this, attains knowledge.
Prajna in deep sleep is M the third part of AUM, concluding the sounds of the earlier two parts. One, who realizes this, attains the compressive understanding of all.
The Syllable AUM in its entirety stands for the fourth state, Turiya the one beyond the phenomenal existence, supremely blissful and non-dual.