Arthur C. Clarke wrote, "Science has recently begun to prove what ancient myth and religion have always espoused: There may be such a thing as a life force."
This "life force" is what Reiki is, in fact it it the Chi in Tai Chi, the Qi in Qi Gong, the Ka in Egypt, the Prana in India, the Eros is Greece. In our language there is no word for it, and that may be a good thing as once it is named it is not that which is named. The pagans still externalize this life force, call it god, construct images of it, conjure a system of illusory beliefs surrounding it, give it a home, and call it heaven.
2,500 years ago Lao Tzu wrote as the first lines of what would later be called the Tao Te Ching:
A way that can be walked is not The Way
A name that can be named is not The Name
In the study and practice of Reiki, which is the Japanese form, the awareness of this life force energy is encouraged by human touch. Each of us have the source of this life force energy deep within us, in the very space separating the atomic particles of our material form. All matter is composed of space, energy, and particles. Sentience adds a dimension to the materiality of a material form, that dimension is what in Latin is called the animus, what we call the animating force of the universe.
The reason we study and practice the Japanese form is that it is the most "other" oriented of all the disciplines. In fact it is less a discipline as it is a celebration, a worship of the divinity within each of us. As we become aware of that inner source we recognize that it has no center, being nothing it cannot exist as something and have a source.