A meditation technique used a great deal in Tibetan Buddhism is uniting the mind with the sound of a mantra. The definition of mantra is “that which protects the mind.” That which protects the mind from negativity, or which protects you from your own mind, is mantra.
When you are nervous, disoriented, or emotionally fragile, inspired chanting or reciting of a mantra can change the state of your mind completely, by transforming its energy and atmosphere. How is this possible? Mantra is the essence of sound, the embodiment of the truth in the form of sound. Each syllable is impregnated with spiritual power, condenses a deep spiritual truth, and vibrates with the blessing of the speech of the buddhas. It is also said that the mind rides on the subtle energy of the breath, the prana, which moves through and purifies the subtle channels of the body. So when you chant a mantra, you are charging your breath and energy with the energy of the mantra, and so working directly on your mind and your subtle body.