Oneness is the nature of the Soul, the Self. Oneness means Advaita or nonduality.+

Sage  Sankara said:~  Talk as much philosophy as you like, worship as many Gods as you please, observe ceremonies, and sing devotional hymns, but liberation will never come, even after a hundred aeons, without realizing the Oneness.

Oneness is the nature of the Soul, the Self.  Oneness means Advaita or nonduality. When the universe appears the duality appears. When there is duality then there is no Oneness. When there is Oneness there is no duality.  

By saying I and you are one the Oneness will not arise.

There is no Oneness in the realm of ignorance.

There is no Oneness when ‘I’ is present.  

There is no Oneness when the mind is present.

There is no Oneness when the dualistic illusion is present.

There is no Oneness when the universe is present.

There is no Oneness when the waking or dream is present.

There is no Oneness when the individual experience of the birth, life, death, and the world is present.  

There is consciousness Oneness in the midst of the dualistic illusion when Advaitic wisdom dawns.

Remember:

All is consciousness.  The whole universe is consciousness. From consciousness, the universe comes. When the universe disappears, the consciousness still remains without form, time and space.

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

Sage Sri, Sankara:~ VC~.63- "Without knowing and examining the external world, one can’t know the Truth, as the idea that the external world exists, won't go. It can go only by an inquiry into the nature of the external world.

After verifying through deeper inquiry if one finds the world is the reality within the illusion then he cannot again say the world is not an illusion.

If one is frightened to accept the world is an illusion (waking) then he is unfit to acquire Self-knowledge or Brahma Gnana or Atma Gnana. 

Those who stuck with the reality of the world are stuck with the reality of the individual experiences of birth, life, and death, which takes place within the unreal world. Thus the pursuit of truth is for those who have the courage to accept the reality as it is, that is the reality without form, time and space.

When you finally realize the Self  ‘is not you but the ‘‘Self’’ is the Soul then you will realize the world in which you exist is merely an illusion created out of the Soul. The Soul is present in the form of consciousness.

Sage Sankara says:~ VC-47-  All the effects of ignorance, root, and branch, are burnt down by the fire of knowledge, which arises from discrimination between these two—the Self and the non-Self.

Till you think you are an individual separate from the world and the world existed prior to you and you are born in it afterward the ignorance will prevail as a reality. Till ignorance is there the universe prevails as reality.

Sage Sankara says: ~ “The exercise in discrimination between real and unreal and renunciation of the false is real meditation, then why you are indulging in other types of meditation.

Perfect understanding and realization of ‘what is what’ leads Self-awareness. By holding onto theories one remains in the realm of duality. You have to mentally go on dropping what is not the truth through deeper Self-search. Finally when you become aware of the fact that, your ego, your body, and the world are one in essence then there is Self-awareness in the midst of duality. : ~ Santthosh Kumaar