PEOPLE today do not know what “correspondence” is. There are many reasons for this ignorance, the primary one being that we have moved away from heaven because of our love for ourselves and for the world. You see, people who love themselves and the world above all focus on nothing but earthly matters because these provide gratification to their more outward senses and pleasure to their moods. They do not attend to spiritual matters because these offer gratification to their deeper senses and pleasure to their minds. So they set such matters aside, saying that they are too lofty to think about.
The early people behaved differently. For them, knowledge about correspondences was the pearl of all knowledge. By means of it, they gained intelligence and wisdom, and by means of it those who were of the church had a communication with heaven. Knowledge about correspondences is in fact angelic knowledge.
The earliest ones, who were heavenly people, did their thinking from correspondence like angels, so they could even talk with angels. Further, the Lord was quite often visible to them, and taught them. Nowadays, though, this knowledge has been so completely lost that people do not know what correspondence is.
from Heaven and Hell, Section 87