Nowadays, though, no one can know about the spiritual things in heaven to which natural things in the world correspond except from heaven, because the knowledge of correspondence has now been completely lost. I should like to present a few examples to show what the correspondence of spiritual things with natural ones is like.
In general, earth’s living creatures correspond to affections, the mild and useful ones to good affections, the fierce and useless ones to evil affections. Specifically, cattle and calves correspond to affections of the natural mind, sheep and lambs to affections of the spiritual mind. Flying creatures, species by species, correspond to cognitive activities of either level of the mind. This is why various animals such as cattle, calves, rams, sheep, male and female goats, male and female lambs, as well as pigeons and turtle doves were accepted for holy use in the Israelite church, which was a representative church. They used them for their sacrifices and burnt offerings, and in these uses they did in fact correspond to spiritual realities that are understood in heaven in accord with their correspondence.
The reason animals are affections, according to their genera and species, is that they are alive, and the only source of the life of any creature is from affection and is in proportion to it. We humans are like animals as far as our natural person is concerned, which is why we are compared to them in colloquial usage. For example, we call a gentle person a sheep or a lamb, a violent one a bear or a wolf, a crafty one a fox or a snake, and so on.
from Heaven and Hell, Section 110