What correspondence is is not known at the present day, for several reasons, the chief of which is that man has withdrawn himself from heaven by the love of self and love of the world. For he that loves self and the world above all things gives heed only to worldly things, since these appeal to the external senses and gratify the natural longings; and he does not give heed to spiritual things, since these appeal to the internal senses and gratify the mind, therefore he casts them aside, saying that they are too high for his comprehension. This was not so with the ancient people. To them the knowledge of correspondences was the chief of knowledges. By means of it they acquired intelligence and wisdom; and by means of it those who were of the church had communication with heaven; for the knowledge of correspondences is angelic knowledge. The most ancient people, who were celestial men, thought from correspondence itself, as the angels do. And therefore they talked with angels, and the Lord frequently appeared to them, and they were taught by Him. But at this day that knowledge has been so completely lost that no one knows what correspondence is.{1} {Footnote 1} How far the knowledge of correspondences excels other knowledges (n. 4280). The knowledge of correspondences was the chief knowledge of the ancient people; but at the present day it is wholly forgotten (n. 3021, 3419, 4280, 4749, 4844, 4964, 4966, 6004, 7729, 10252). The knowledge of correspondences flourished among the Eastern nations and in Egypt (5702, 6692, 7097, 7779, 9391, 10407). 88. Since, then, without a perception of what correspondence is there can be no clear knowledge of the spiritual world or of its inflow into the natural world, neither of what the spiritual is in its relation to the natural, nor any clear knowledge of the spirit of man, which is called the soul, and its operation into the body, neither of man's state after death, it is necessary to explain what correspondence is and the nature of it. This will prepare the way for what is to follow. 89. First, what correspondence is. The whole natural world corresponds to the spiritual world, and not merely the natural world in general, but also every particular of it; and as a consequence everything in the natural world that springs from the spiritual world is called a correspondent. It must be understood that the natural world springs from and has permanent existence from the spiritual world, precisely like an effect from its effecting cause. All that is spread out under the sun and that receives heat and light from the sun is what is called the natural world; and all things that derive their subsistence therefrom belong to that world. But the spiritual world is heaven; and all things in the heavens belong to that world.