The recitation and repetition of specific mantric codes is an accelerant to transform habits, insecurities, things you think about yourself - to leave behind so you can become YOU.
There are eighty-four points in the upper part of the mouth and the touch of the tongue works like acupressure. When you speak, this tongue touches those areas and stimulates the nervous system and brain. The words we call mantra are designed to stimulate a particular combination of meridians in the mouth. These words also have a projective power. The theory is that the huge computer mind is Infinite and our mind is limited. If you know the combination of the frequency of the signal which can tap the resources of the Infinite Mind, then the flow of Infinity will start appearing to your finite mind. Mantra is nothing but a telecommunication of the finite unto the Infinite. The individual creates a frequency of vibration within his electro-magnetic field to tap the electro-magnetic field of the Universe. - Yogi Bhajan
Because the reflex points are stimulated by the movements of the tongue, you get the maximum benefit from the pattern of a shabad by consciously repeating the sounds out loud. That is called jappa -
conscious, conscientious, recitation.
rotating the tongue over the 84 reflex points in the pattern of the shabad produces the maximum impact on the gross level of the neuro-endocrine system. as the shabad gets established in the nervous system and your subconscious, every cell of your body will vibrate the pattern with you.
The techniques of the Shabad Guru codified in the mantras of Kundalini Yoga wait for us to mine their secrets. Every person can use them to elevate themselves, to heal, to develop stamina, to increase intuition. They do not need to know the science of the process. They only need to apply the technology of the Shabad Guru.