A definition of a mantra is "that which protects the mind" which in this case protects your own mind from negativity. When you are nervous, disorientated or emotionally fragile doing simran, reciting a mantra inspiringly can change the state of your mind. A Mantra is the essence of sound, and the embodiment of truth in the form of sound. Each syllable is impregnated with spiritual power, and vibrates with the blessing of the speech of the Gurus.