Nanu sāhankārasya kiñcijjñasya jīvasya nirahankārasya sarvajñasyaīśvarasya tattvamasīti mahāvākyāt kathamabhēdabuddhiḥ syādubhayōḥviruddha dharmākrāntatvāt.
From the sentence (which reveals the oneness between the individual and the total), “You are That”, how can there be the knowledge of non-difference between the two - jīva who has the I-notion, who is of limited knowledge, and Īśvara who is devoid of ego, who is all knowledge - because the two (jīva and Īśvara) being possessed of contradictory qualities?
Teaching of all the Upanishads have the culmination in revealing the oneness between Jīva and Īśvara. Jīvātmā and paramātmā are one and the same original consciousness alone. The statement reveals this oneness is called Mahā-vākayam, can be called as the great equation. One of the famous one is "Tat Tvam Asi" found in Chandogya Upanishad. Tat means that paramātmā-the cosmic intelligent. Tvam means you, refers to each of us, the individual jīvātmā. And Asi means "are". The entire sentence means "You are That". When the student listens to the Mahā-vākayam, what will the student think? Therefore the student raises the objection "nanu", like "objection". How can there is vision of equality between the paramātmā having superior attributes and Jīvātmā having the inferior attributes.
Iti cenna. Sthūlasūkṣmaśarīrābhimāni tvampada vācyārthaḥ. Upādhivinirmuktaṁ samādhi daśāsampannaṁ śuddhaṁ caitanyaṁtvampada lakṣyārthaḥ. Evaṁ sarvajñatvādiviśiṣṭa īśvaraḥ tatpadavācyārthaḥ. Upādhiśūnyaṁ śuddhacaitanyaṁ tatpada lakṣyārthaḥ. Evaṁ ca jīveśvarayōḥ caitanyarūpeṇā'bhede bādhakābhāvaḥ
If it is so (if that is your argument), no (there is no real difference). The immediate meaning of the word “you” is the one who is identified with the physical and subtle bodies. The implied meaning of the word “you” is pure consciousness, the one who is free from the limiting adjunct, the one who obtains during an experience of subject-object resolution. Similarly, the immediate meaning of the word “tat”, that is the Lord, the one who is endowed with all knowledge, etc. The implied meaning of the word “tat”, that is pure consciousness, free from limiting adjuncts.
And thus, between jiva and Isvara (individual and total) there being no difference in the form of consciousness, (there is) nothing to negate that.
In any equation, there is a seemingly different between two which are equated, otherwise equation is not necessarily. For example a very simple 3+2 = 6-1. Non of the four numbers are the same. This equation is obvious for us, but not for a kindergarten kid. Therefore the teacher explain the meaning of this Mahā-vākayam - great equation by explaining the lakṣyārthaḥ - implied meaning and vācyārthaḥ - immediate meaning.
When the word "pillar" is told, what is understood in your mind is a tall vertical structure of stone, wood, or metal, used as a support for a building, or as an ornament or monument. It is the vācyārthaḥ - immediate meaning of the word "pillar", an inert object. But the same word also can be use for a sentient being like "he is the pillar of the family". In this case, lakṣyārthaḥ - implied meaning is to be conveyed. Taking the nature of the pillar as "support" and giving up the inert quality for the implied meaning here. Only one who is equipped with the knowledge of the nature of the word which is conveyed, then one can take the appropriate meaning according to the context.
Therefore Mahā-vākayam "tat tvam asi" is told only after the enquiry of the individual and total are done. When "you are that" is said, the equation between you who is included the micro medium consist of three bodies and that Īśvara is endowed with macro medium, the intelligent behind all these creation, can not be done.
The meaning of tvam here in this equation, is the consciousness principle which the three bodies are depend upon to exist, and the meaning of tat is the same consciousness principle which the entire manifestation is depend upon. There is no contradiction in this sentence of great equation.
Therefore in this equation, the medium (upādhi) of both sides need to set aside or separated. This separation can not be done physically, and only can be done cognitively.
Just like after knowing the falseness of the mirage water, one will not go after it, but one still perceived it as mirage water. This is the Tattvabodha - self knowledge.