91. Such being the difference between the heat and light of the two worlds, it is very evident why those who are in the one world cannot see those who are in the other world. For the eyes of man, who sees from natural light, are of the substance of his world, and the eyes of an angel are of the substance of his world; thus in both cases they are formed for the proper reception of their own light. From all this it can be seen from how much ignorance those think who, because they cannot see angels and spirits with their eyes, are unwilling to believe them to be men.