The syllable “Om” or “Aum” is of paramount importance in Hinduism.
Traditionally in India, AUM is the third aspect of the three-fold nature of God or Satchidananda (Sat, ever-existing; Chid, ever-conscious; Ananda, ever-new joy). This three-fold nature is called as Sat, Tat, and AUM. Sat represents the God beyond creation, uninvolved and unknowable through ordinary human consciousness. Sat is universal, timeless, formless, omnipresent, omniscient, and omnipresent.
When God (Sat) manifested the universe, the only “building blocks” available were movement, since before that, there was only oneness or perfect stillness. Thus, that one, unmoving Presence “moved” or vibrated and thus creating Maya, or opposites, such as left and right; up and down; in and out, darkness and light, and so on. This movement or vibration among opposites is called AUM or sometimes called the Divine Mother. Through the Divine Mother (AUM) was born the second aspect called Tat, the Son of God or Christ Consciousness, which represents the presence of God within all creation.
Sat: God beyond creation
Tat: God within creation
AUM: The cosmic vibration, making it all possible