What is the principle of life?

What you term matter is only one of the forms in which spirit—or better, the principle of life—manifests itself. It is the most real of all forms to you who dwell in the realms of such manifestations, of course, because the most tangible—because, in short, it is that of which you are a part, a fraction, a unit. When you escape from that form to one more condensed, refined, you may wonder how anything so coarse, thin, vapory, as what you call matter, could seem solid, tangible, real!