The Upanishads present a profound exploration of ultimate reality and the nature of the self. They teach that beneath the changing world lies Brahman, the eternal, infinite, formless ground of all existence, and that the true Self, or Atman, is not the body or mind but this very same reality. This identity of Atman and Brahman is expressed in great declarations such as “Tat tvam asi” (“Thou art That”) and “I am Brahman,” affirming a fundamental unity at the heart of all being. The phenomenal world, with its multiplicity and change, is described as veiling this truth, giving rise to the appearance of separation and obscuring the underlying oneness.

Within this vision, the Upanishads also articulate the law of karma and the process of reincarnation, in which actions shape future experiences and births. Existence in the cycle of birth and death, or samsara, continues so long as ignorance of one’s true nature persists. Liberation, or moksha, is described as freedom from this cycle, attained through direct knowledge of the Self as Brahman. This realization dissolves the bondage created by ignorance, fear, and attachment, and is supported by a life grounded in dharma, including truthfulness, non-violence, self-discipline, and inner purity.

To prepare the mind for such realization, the Upanishads emphasize meditation, self-inquiry, and contemplative disciplines. They speak of focusing on Om as a sacred sound that symbolizes the cosmic principle and serves as a means of spiritual insight. Various states of consciousness—waking, dreaming, and deep sleep—are examined to point toward a transcendent “fourth” state beyond them, in which the Self is directly known. Through renunciation, detachment from worldly desires, and sustained inner practice, the seeker is guided from outward ritual to inward realization, from mere belief to experiential knowledge of the unity of Atman and Brahman.