One of the shortest Upanishads—yet highly profound—the Mandukya, in just twelve verses, presents “Om” through three perspectives:
Om — The Macrocosmic
The introduction verse describes Om at the cosmic level as encompassing four spans:
- Past
- Present
- Future
- Beyond Time
Om — The Microcosmic
The text then turns inward, stating that the Inner Divine has four experiential aspects:
- Vaiśvānara — waking state
- Taijasa — dream state
- Prājña — deep sleep state
- Chaturtham (the Fourth) — the Inner Divine
Om — The Syllable
Finally, the Upanishad links the four experiences to the sound-units of Om:
- A-sound — waking
- U-sound — dreaming
- M-sound — deep sleep
- Silence after Om — Chaturtham, the Fourth
Thus expounds this scripture, affiliated with the Atharva-Veda. For the actual verses and additional insights from the author in the footnotes, refer to the translation PDF (book).