609. The three levels on which the heavens exist, and therefore on which the human mind exists, can to some extent be illustrated by physical things in our world. The three levels are like the relative differences in value between gold, silver, and copper. (The statue of Nebuchadnezzar, Daniel 2:31 and following, is another analogy that uses these metals.) These three levels are as different from each other as a ruby, a sapphire, and an agate are different in purity and value. An olive tree, a grapevine, and a fig tree would be another set of examples; and so on. In fact, in the Word, gold, a ruby, and an olive tree symbolize goodness that is heavenly, the type of goodness found in the highest heaven; silver, a sapphire, and a grapevine symbolize goodness that is spiritual, the type of goodness found in the middle heaven; and copper, an agate, and a fig tree symbolize goodness that is earthly, the type of goodness found in the lowest heaven. (I have shown above that the three levels are the heavenly, the spiritual, and the earthly.)