When the universe appears to us as a gigantic void in which the matter that makes up suns and galaxies takes up extremely little of this space, it is absolutely not because it really is such an empty space but because matter occurs in a state here that cannot affect physical senses.
      Thus we see here two kinds of matter: that which is visible to the senses and that which is invisible. But just as visible matter constitutes the visible world, so does invisible matter constitute an invisible world. And here we have arrived at the foundation of every religion, namely that a "spiritual" world exists beyond the physical. But for us the invisible or spiritual world is thus not a belief or a hypothesis but a realistic fact.
      Why is this invisible world described as "spiritual"? It is described as spiritual because our entire consciousness and world of thought is built up of this matter. With physical senses or eyes we cannot see our thoughts or ideas. For this reason we must express ourselves by means of a language. If our thoughts were visible just like our physical organism, like our eyes, hair and hands and so on, we would not need to use speech. Since thoughts are the same as consciousness, and consciousness in its turn is the same as spirit, and spirit belongs under invisible matter, we have here the reason why this area of matter has been called the "spiritual world".