What was the central message of the Upanishadic mantra tat tvam asi?

The central message of the Upanishadic mantra “tat tvam asi,” which translates to “that thou art,” conveys the profound philosophical idea of the unity between the individual self (Ātman) and the ultimate reality or universal consciousness (Brahman). This mantra emphasizes the belief that at the core of existence, there is a fundamental oneness that transcends individual identity, encouraging seekers to realize their true nature and the interconnectedness of all beings. It serves as a key teaching in Vedanta philosophy, guiding individuals toward self-realization and spiritual enlightenment.