Students often ask, "Why do we chant Aum at the start of class?" Sometimes people go through years of chanting without knowing why. The mantra will do it's work regardless of understanding, but it's always nice to deepen our knowledge. My Guruji said this about the practice of repeating the mantra Aum, known as Aumkaara.
Aum is a single syllable Mantra representing the Ultimate Truth, Naada BrahM.
Guruji Shri Shriyogeshwaraji
I start every class I teach with Aumkaara. Guruji has said that it can do more for balancing the Pranas, energies of the body, than extended periods of Pranayams and other Hatha practices.
Here is a further quote from the commentary on the Hatha Yogapradipika:
The universal mantra that can be used by everyone is Om, comprised of the sounds 'A'. 'U', and 'M'. It is the cosmic vibration of both the manifest and unmanifest realities. 'A' represents the conscious world and creation, 'U' represents the intermediate realms and subconscious, and 'M' represents the unmanifest and unconscious. The three sounds together represent the existence of the supreme consciousness and manifestation. Everything in creation has its own particular vibrational frequency and mantra, but the combination of the whole universal and vibrational frequencies pulsates to the rhythm of Om. There is no greater mantra to repeat.
As always, do not start or practice a mantra without the guidance of your Guruji, or a teacher who has been authorized by their Guruji. While mantras can lead to ultimate liberation, when misused will lead to pain and sickness.
Jay Shiv Shakti