Yoga and modern western science both state the universe and all it entails is pure energy. And this energy is constantly in flux.
Thus both views hold there is nothing truly static about the universe, which includes ourselves.
There are two important things to understand about the nature of energy.
First, energy has many manifestations. Thought, emotion, sound, light, heat and movement are all examples of energy manifesting.
Second, energy affects energy. This notion is simple to see if one places a hot flame under a pot of water. The energy of the flame (manifesting as heat and light) would excite the energy of the pot and then the energy of the water, bringing the water in the pot to an eventual boil.
These two important aspects of energy's nature are the understanding upon which the practice of sound yoga is based.
The sounds used in sound yoga practices are referred to as mantras. Mantra is a Sanskrit term that literally translates as MAN, to think, and TRA, to free oneself.
Thus mantra practice is the active or conscious use of thought or energy to free oneself from dukha (suffering), and bring one to enlightenment (the experience of the True Self).
It is important to remember however, that for a mantra to be of its full holistic effect, it must be used consciously.
Chanting or repeating mantras without mindful understanding of its meaning and purpose does not affect deep change in both the conscious and unconscious mind.
This should be remembered especially when the repetition of the mantra is long and continuous, such as in the case of japa meditation.
Here it is easy to allow the mind to wander and have the mantra become a simple unconscious hypnotic trance.
The need to stay present and mindful is as important in your mantra practice as it is in every other aspect of your yoga practice.