91. Since there is such a difference between the heat and light of the two worlds, it is clearly apparent why it is that people who live in one of these worlds cannot see those who live in the other world. For the eyes of a person who sees by virtue of natural light are formed from the substance of his world, and the eyes of an angel are formed from the substance of his world, so as to be suitably formed in each world to receive their own light. It can be seen from this how ignorant the thinking is of people who do not accept into the tenets of their faith that angels and spirits are people, because they do not see them with their eyes.