Mantras themselves have vibrations, so when you repeat them, even mentally, they produce a kind of vibration within the body. They shake, they vibrate the entire body—all the molecules, all the cells of the body—and they rearrange your entire personality, they tune your personality. After a certain amount of practice, the entire body begins to vibrate in the same wavelength. And because mantras are the divine part of the cosmic vibration, when your system begins to vibrate in that wavelength, you will begin to communicate with similar vibrations in the cosmos. This is what you call communication with God. Yes, mantras have certain special powers; they’re not just meditation alone. For the sake of meditation, though, you can use any mantras you want. Just make sure that the mantras you choose will always elevate you.
– Sri Swami Satchidananda