Why do we use mantra?

‘Chanting mantras, either silently or out loud, is a consicious method of controlling and directing the mind. Happiness, sorrow, joy and regret are vibratory frequencies in the mind. Call them attitudes, or beliefs, but fundamentally, they are vibratory frequencies or thought waves. They determine the kind of programme our mind plays.’
‘Mantras are formulas that alter the patterns of the mind and chemistry of the brain, according to physical and meta-physical laws. The power of a mantra is in its sound vibration. The mantras used in Kundalini Yoga elevate or modify consciousness through their meaning and rhythmical repetition. It is beneficial to link a mantra to the breath.’
(From The Acquarian Teacher, 3rd Ed., 2005)