I explained above (Section 548) that evil spirits voluntarily throw themselves into hell, so I need to state briefly why this happens when there is such torment in hell.
From each hell there breathes forth an aura of the cravings that obsess its inhabitants. When this aura is sensed by people who are obsessed with a similar craving, it touches their hearts and fills them with delight because the craving and the delight are inseparable—whatever we crave is delightful to us. This is why spirits turn in that direction and are impelled there by their hearts’ delight. They do not yet realize what kind of torment there is in hell, and the ones who do know still feel the craving. In the spiritual world we are all incapable of resisting our impulses because the impulses come from our love and the love comes from our intent and the intent comes from our nature, and we all act from our nature there.
So when spirits voluntarily or freely arrive at their hell and go in, they are accepted cordially at first and think they have arrived among friends. This lasts only a few hours, though. All the while they are being probed to find out how crafty they are, and therefore how powerful. Once this probing is complete the attacks begin in various ways, getting more and more severe and intense. The intensification is effected by their being taken farther and deeper into hell, since the farther and deeper you go there, the more malevolent are the spirits. After these attacks, the malevolent spirits begin to torment the newcomers with punishments until finally they are reduced to slavery.
However, since rebellious movements are always arising (everyone there wants to be greatest and burns with hatred against everyone else, which keeps generating new attacks), the scene is constantly changing. The people who were enslaved are released and offer their support to some new devil for the subjugation of others. Then the ones who do not surrender and yield their obedience are tortured in various ways, and so on and so on.
Torments like this are the torments of hell that are referred to as hellfire.
The gnashing of teeth, though, is the constant clash and strife of false convictions with each other (and therefore the warfare of the individuals who hold the false convictions) united to contempt for others, hostility, derision, mockery, and blasphemy. These even break out into various kinds of butchery. Everyone there is defending his or her own false convictions and calling them true. From outside the hells, these clashes and battles sound like gnashing teeth, and they turn into the gnashing of teeth when truths from heaven flow into hell.
In these hells dwell all the people who acknowledged nature and denied the Divine. The people who deliberately convinced themselves are in the deeper hells. Since they cannot accept any ray of light from heaven and can therefore not see anything within themselves, most of them focus on their senses and their bodies. These are people who do not believe anything they cannot see with their eyes and touch with their hands. So for them, all sensory illusions are the truths on which they base their arguments. This is why their arguments sound like the gnashing of teeth. It is because in the spiritual world all false statements grate, and teeth correspond to the outmost aspects of nature and to our own outmost natures, which have to do with our senses and our bodies.
On the gnashing of teeth in the hells, see Matthew 8:12; 13:42, 50; 22:13; 24:51; 25:30; and Luke 13:28.
from Heaven and Hell, Sections 574-575
Section 548: Published 1/9/2019