All perfection increases as we move inward and decreases as we move outward, because more inward things are closer to the Lord and intrinsically purer, while more outward things are more remote from the Lord and intrinsically cruder. Angelic perfection consists of intelligence, wisdom, love, and everything good, with happiness as their result. It does not consist in happiness without these former qualities, since happiness without them is merely superficial, with no depth.
Since the inner reaches of angels of the central heaven are opened at the third level, their perfection far surpasses that of angels in the intermediate heaven, whose inner reaches are opened at the second level. By the same token, the perfection of angels of the intermediate heaven surpasses that of angels of the outmost heaven.
Because of this difference, an angel of one heaven cannot gain admission to angels of another heaven: someone from a lower heaven cannot come up, nor can someone from a higher heaven come down. Anyone who comes up is seized by anxiety even to the point of pain and cannot see the people who are there, let alone talk with them. Anyone who comes down from a higher heaven loses his or her wisdom, stammers, and loses confidence.
There were some people from the outmost heaven who had not yet been taught that heaven is a matter of angels’ deeper qualities, but believed that they would find greater angelic happiness if only they were admitted to the heaven where these angels lived. They were allowed to visit them, but when they arrived, even though there were a great many angels there, they did not see anyone no matter where they looked. The deeper levels of the newcomers had not been opened at the level where the more inward angels lived, so they had no sight. Before long, they were seized by heart pain and eventually could scarcely tell whether they were still alive or not. So they quickly made their way back to the heaven they had come from, and were delighted to be among their own people. They vowed that they would never again crave conditions that were higher than the ones that suited their own way of life.
It is different when the Lord raises people from a lower heaven into a higher one so that they can see its splendor, which happens quite often. Then they are prepared in advance and provided with mediating angels who serve as agents of communication.
We can see from all this that the three heavens are quite distinct from each other.
from Heaven and Hell, Sections 34, 35