According to the Vajrayanists mantra is endowed with great power and can even confer Buddhahood. A sound-symbol becomes mantra becomes mantra only when a Guru administers it to his disciple at an initiation ceremony.
Each word is a sound equivalent of an experience of reality. Experience of a higher order cannot be effectively expressed or re-enacted through concepts; but through sound-symbols it can be. These sound symbols are not arbitrarily created outside such experiences but they are spontaneous expressions, springing forth from the deepest recesses of the human psyche during such an experience. They convey an experience of reality that cannot be translated into concepts. When a mantra is uttered it calls forth its content into a state of immediate reality. Hence, mantra is not mere speech but power it does not speak but acts. Mantra is not only an expression of the non-dual experience of reality but also means of identification and introjection of that very same reality.
Mantra is not a plea or prayer to some deity in the heavens to act in some miraculous way. The power of the mantra is self-generated. Mantra disposes the sadhaka to a psychic disposition by which he evokes from within his own consciousness the deity as well as its power. The mantra formulas namely, form, feeling and idea. The mantra should be melodious, rhythmic and forceful in form. The feeling aspect is the devotional impulse expressed in faith, love and veneration. The idea is constituted of the mental associations; knowledge and experience which arouse intensify and transform the latent psychic forces. The actual mantra is not the physical sound; it is not uttered by the mouth nor heard by the ear; it is spiritual, uttered by the mind and heard by the heard by the heart. According to the Vajryanists it has been said that for mantra to be effective must be learned from a competent Guru and requires constant practice.
Mantra purges the mind of concepts and categories and heals it of its constructive tendencies; it becomes a psychic tool in the whole dialectical process. The meaning of the mantra is more than the sum of its parts. It is meaningful not from a discursive or descriptive point of view, but in all persuasive holistic sense.
Hence it can be concluded saying that mantra is a symbol, it is an inner vision of Ultimate Reality persuading the sadhaka to that Reality. The emotive and the psychic effect of the mantra lead the sadhaka to the depths of non-dual consciousness.