" that in the whole range of speech there is but one name which is distinguished by its very nature from all other names. This is the name “I.” Every other name can be applied by any one to the thing or being to which it belongs. The word “I,” as the designation of a being, has a meaning only when given to that being by himself. Never can any outside voice call us by the name of “I.” We can apply it only to ourselves. I am only an “I” to myself; to every one else I am a “you,” and every one else is a “you” to me. This fact is the outward expression of a deeply significant truth. The real essence of the ego is independent of everything outside of it, and it is on this account that its [pg 031] name cannot be applied to it by any one else. This is the reason why those religions confessions which have consciously maintained their connections with occult science, speak the word “I” as the “unutterable name of God.” For the fact above mentioned is exactly what is referred to when this expression is used. Nothing outward has access to that part of the human soul of which we are now speaking. It is the “hidden sanctuary” of the soul. Only a being of like nature with the soul can win entrance there. "
― Rudolf Steiner , An Outline of Occult Science