When the man of wisdom discriminates between what is existence— awareness—and what is not, he ascertains that reality through the perception of true understanding and insight. He knows that his Self is of the nature of endless knowledge, becomes free of both existence and nonexistence, and is established in a state of peace within.
The Vivekachoodamani of Sri Adi Sankaracharya explains this as the state of Nirvikalpa Samadhi or a state of mind where there is no change or modification that is experienced. When this state of mind is experienced, the knots of ignorance in our feelings loosen up completely. As a result, one experiences the Self that has no duality.
All notions of you, I, this etc are just imaginations due to the inherent flaw of the discriminating intellect. These false notions arise due to ignorance as the reality of the Self within is not just non-dual, but free from any speciality too. It is the same in all. In the state of meditation where the mind goes through zero changes, this state of experience presents itself.
This state of experience of the oneness is achieved by a certain calmness of mind, control of sense organs of perception and action, a supreme withdrawal from all activities except one’s own duties and patience. Such a person experiences his own Self as the Self in all. Through this means, all the modifications caused by ignorance of the awareness, the desires generated as a result and the actions that are performed to fulfil those desires are burnt in the fire of consciousness. The person, though he may be in the physical form, experiences the immortal form of formlessness and thus is happy, free of all compulsory action and modifications of the mind.
In a very peculiar statement, the Acharya says that it is only that person, who is able to integrate his mind and offers the objects of the sense organs to the consciousness within, will be freed of the bondage of existence. It is not for those who simply talk about what is mentioned in the scriptures. This is a clear indication that the experience of the Self happens not just by knowledge and prattling but by dedicated hours of practice of Samadhi.
The difference between what is the Self and what is not, happens due to the conditioning of the body, mind and intellect. With right understanding if the conditioning is removed, then the Self alone exists. Therefore, to achieve the goal of removing these conditioning notions, the wise seeker may be seated in the state of unchanging absorption in the Self—Nirvikalpa Samadhi.