The basic teachings of the Upanishads are summed up in six great sayings (Mahavakyas). These are----
"I am Brahman" (Aham Brahmasmi). This states the identity of the inmost consciousness of the individual with that of the supreme Divine. The ultimate truth of Vedic knowledge is not that some great savior is God or the Lord or that such and such a God or name and form of God is the supreme. It is not the worship of a person, book, image or idea. It is not even the worship of God. The Upanishads say that whatever we worship as truth apart from ourselves destroys us. They teach that our own Self is the true Divinity, that it is the presence of the absolute within our heart and all the universe.
"The Self is Brahman" (Ayam Atma Brahma). This also states the identity of the soul with the Absolute but in a more objective and less direct manner. Not only is our Self the Divine. It is the same Self in all beings that is the same Absolute truth.
"That thou art" (Tat tvam asi). Whatever we see or think about we are that. Not only is the I That, the You is also That. We are that ultimate I and Thou in all. The consciousness in the other is also the Divine.
"Intelligence is Brahman" (Prajnanam Brahma). Our discernment of truth is the truth itself. It indicates that the Divine intelligence is present within us and has the power to return us to the Divine. Our inmost intelligence is that supreme intelligence through which we can merge into the Absolute.
"The Universe is Brahman" (Sarvam Khalvidam Brahma). The entire universe is the Divine, which includes our self. The Divine is not only the consciousness principle in you and I, it is also the being principle in all things. It is the ultimate object as well as the inmost subject in all beings. It is one and all and all in one.
"He am I" (So'ham). This shows the identity of the self with the Divine Lord inherent within the natural movement of our breath. "So" is the natural sound of inhalation, "ham" of exhalation.
These are statements of the identity of the individual consciousness with the Absolute or Divine reality. They all derive from and merge into Om (AUM), the Divine Word of "I am all".
Source David Frawley : From the River or Heaven