The Mahavakya Tat Tvam Asi occurs in the Chandogya Upanishad. Aruni, a great sage, teaches his son Shvetaketu that Brahman is the ultimate source of all the individual beings. Then he put the very essence of his teaching in the following words – Now, that which is the subtle essence – in it all that exists has its Self. That is the truth. That is the Self. Thou art That (Tat Tvam Asi), Shvetaketu.
Swami Vivekananda in his lecture ‘The Free Soul’, has put forward the Vedantic position on the Nature and the Soul scientifically. The Sankhya philosophy says that there are two absolutes – Nature and Spirit. However, the Vedantists argue that there cannot be two absolutes. According to them, the sentient power (God) is the motive power of insentient Nature which undergoes modification.
Also, Vedanta teaches that God is not just the instrumental cause of this universe, but also the material cause. That means, it is God himself, who has become this universe. Then, what about the individual souls that are sentient? One explanation is thatsouls are also part of God. Swami Vivekananda scorns at this idea – ‘What is meant by a part of the Infinite? The Infinite is indivisible; there cannot be parts of the Infinite.’ He further declares that only the Advaitisit solves this problem, by maintaining that each souls is really not a part of the Infinite, but actually is the Infinite Brahman. The appearance of division that we find in this material world is only a delusion caused by limitations of Time, Space and Causation.
Swami Vivekananda calls upon humanity to understand the above truth and discover the divinity within” – There is but one Infinite Being in the Universe, and that being appears as you and I’.
The dualistic schools of Vedanta are of the opinion that the universe comprises the eternal God and the infinite number of souls. Swami Vivekananda counters this with the following arguments – The effect is nothing but the cause in another form. If the universe is the effect, God is the cause. So, it is safe to say that it is God Himself who has become this universe. Then everything is God.
Regarding the individual souls, an Advaitist says that in reality, there is no Jiva at all since the very idea of the universe is an illusion, a dream. But a dream cannot be without a reality and that reality is the one Infinite Existence. The Jiva is but a reflection of this Reality. It is God who is being reflected in all these different Jivas.
When more and more people realize this truth, a reign of peace will dawn on the earth and the universe will then be a playground. Then no one will look down on another. Instead of throwing hatred, jealousy and evil thought, people will think ‘it is all He’. Swami Vivekananda says that this is the great utility of divine realization.
Swami Vivekananda says that these thoughts were worked out amongst individuals in India in ancient times. They are the common property of the saint and the sinner, of men and women and children, of the learned and of the ignorant. Swamiji prophesies that these thoughts will be broadcast over the whole world – they will then permeate the atmosphere of the world, and the very air that we breathe will say with ever one of its pulsations, ‘Thou art That (Tat Tvam Asi).’ And the whole universe with its myriads of suns and moons, through everything that speaks, with one voice will say, ‘Thou art That (Tat Tvam Asi)