Alphabe Thursday … U is for Upanishad.

“Verily, this entire [world] is the Absolute (brahman). Tranquil, one should worship it [through contemplation] , for one comes forth from it” Chandogya-Upanishad (3.14.1)

U is for Upanishad; in particular the Chandogya which comes from the words chandas meaning hymn (lit. pleasure) and ga – going referring to the brahmins who sang the hymns of the Sama-Veda during the sacrificial ritual of vedic times.
The Chandogya Upanishad consists of the esoteric teachings of the chandogya; the vedic chanters.
The scripture begins with the elaborate speculations about the sacred syllable Om the most celebrated numinous sound or mantra of Hinduism.
The syllable Om has a long history that dates back to Vedic times (1500 BCE) It was used at the beginning and the end of ritual pronouncements; rather like the Christians use Amen.
The Om is regarded as a divine revelation.  The yogis more recently describe how in deep states of meditation they can hear the sound vibrating through the entire cosmos.  This compares with the Pythagorean and Neoplatonic thought in the notion of Music of the Spheres, the cosmic harmonic generated by the motion of heavenly bodies.