According to the Hindu Mandukya Upanishad,whichis entirely devoted to the explanation of the syllable, "Om is the one eternal syllable of which all that exists is but the development. The past, the present, and the future are all included in this one sound, and all that exists beyond the three forms of time is also implied in it". Although Om symbolizes the most profound concepts of universal creation including the three stages of existence (birth, life and death), it is in use daily. The devout begin their day, work, prayers or a journey by uttering Om, the symbol is enshrined in every Hindu temple and it is often found at the head of letters and at the beginning of important documents. Many wear the sign of Om as a pendant, and it is the first syllable of the sacred mantra "Om mani padme hum".