This is one of the best explanations I've found regarding the phrase Om Tat Sat Om. There are many sources on the net that can give you additional information. To me, with my admittedly limited understanding, it is the Sanskrit equivalent of "I Am That I Am." We are ultimately all ONE. "The very ancient Sanskrit phrase "Om tat sat" has been translated in many ways, such as "Thou are that" and "I am that." "Sat" stands for truth, being, or reality. "Tat" stand for "that." "Om" is said to be the sacred syllable. The seed sound that is the source of all other sounds. Some say "Om" or "Aum" is the primal sound of the universe -- there at the moment of creation. Someone called it the "dial tone of the universe." This ancient phrase suggests that we attend to our sense of "I am" or "self-existence." It's that simple, yet profoundly difficult because of all that distracts us from the sense of existence from moment to moment." If we spent more time concentrating on how we're alike than how we're different, the world would be a more peaceful place. Just my humble opinion.