How do mantras work?
Everything in the Universe is made of energy. Energy vibrates on a particular frequency. The difference comes from different vibrational frequency. Sounds are audible vibrations. Thoughts are electromagnetic vibrations or silent sounds. Mantras are used to affect the consciousness through sound. "MAN" means mind, "TRA" means wave or projection. We tune into universal vibrations and change our frequency by chanting mantras. When we chant, our whole being resonates with that frequency. Our energy tunes in and synchronizes with the energy fo the sounds and thoughts we produce. The nature of our energy attracts corresponding events and circumstances in our lives.
Chanting mantras is a conscious method to direct the mind in a particular way. By using mantras we make a choice to vibrate a positive power contained in them. Most of what we create or attract is predetermined by our subconscious programming. Mantra is a powerful tool to "re-program" ourselves and clear the subconscious to create new thought patterns. Additionally, mantras open those mind channels to us that usually are not accessible through rational mind.
Yogi Bhajan's video on the power mantra.