MANTRA

A mantra is a sacred saying, usually pronounced silently, mentally.  The word mantra means "thought form."  A mantra may be only a single syllable, such as Om, Srim, Aim, Hrim, etc., or be several syllables, or many. 

Each deity is represented by its own mantra.  Only the correct enunciation of the correct mantra will result in a deity entering its image where it will respond to a devotee.  As the word form of one's personal god, a mantra has considerable potency.   A mantra may even represent the Divine Being Itself, Brahman.  Brahman's mantra is OM, and typically is verbalized. 

Rishi's, or seers, were the original receivers of mantras, who then passed them down to their devotees via their gurus.  The devotee must keep his mantra secret, saying it silently as part of his regular worship.  Other mantras, such as OM, are openly known.  Repetition of the mantra (japa), performed regularly and reverently, will result in purification of the mind and ultimately in God-realization.