The central theme of Bhagavad-Gita is ‘tattvamasi. Here is the teachings of the Upanishad that implores the students to realize the Self. Knowledge of the Self or Atmajnyan is very important. All the worldly attainments, may it be a Nobel prize or a national honour of Bharata Ratna (or an accreditation, a scroll of Paper with some money), it’s all a waste if the recipient dies without knowing who actually he or she is! It is like the adage, “Lo, there goes the celebrity who is known all over the world. Alas, it is a great tragedy that he knows not who himself is! The entire life in human form is a waste if one dies without knowing what this jiva is and how it came to take this form. It is thus essential to realise the true nature of the self.

   Tat tvam asi is the Vedic statement where the perceiver and the perceived become one. Sage Aruni Uddalaka advises his student Shvetaketu to realize who he is. The student must realize the self by contemplation, meditation. Meditation is actually dwelling in the Self, the Brahman. Atman and brahman are one: atma eva brahma. Atma is omniscient; atma knows all. ayam atma brahma says the self. Finally, one realizes the fact that everything is Brahman. sarvam khalvidam brahma; there is nothing besides brahman since brahman is interwoven into the fabric of cosmic existence. "Brahman only exists and nothing else" and Shree Krishna is that (tat) nirakara parabrahman. 

 Lord Shree Krishna imparts this divine secret knowledge to Arjuna. He elaborates the ‘tvam’ (you/Arjuna) aspect  in the first six Chapters; and, goes on to say who He is (Tat aspect) in the next six chapters. Finally He teaches how to unite this tvam and tat by ‘asi’ in yoga in the last six chapters. By the time one comes to the end of Bhagavad-Gita anushthana with full devotion, the sadhaka attains to the state of oneness with the lord. He will be liberated from further embodiment. It is mukti to a jiva that was hitherto taking repeated births in ignorance.