Burning Off Sin
Angels are highly concerned with the right and true path. This is not purely based on just their self-righteous perspective though. What they consider sin is literally a threat to their very existence. There are strict, strict rules to prevent sin, to guard themselves against the corruption of its influence. For, if they slip into evil, in their intentions, their mind, their soul, their actions, in any way…they will begin to be corrupted. It is unclear exactly what it is that begins this corruption, whether it be a constant in every instant to certain acts or whether it’s more to do with the state and intention of the individual. All that is known is that it will kill them.
(In reality, it is a mixture of true evil intentions, perception of the angel as to what is wrong, and of their individual negative feelings about an act that corrupts them. Like guilt. Guilt will corrupt them. They just don't know and no one else does either.)
Sin accumulates the more it is done and the corruption does not go away on its own. It also perpetuates itself, meaning that the desire to continue to sin grows the more they succumb and do it in the first place. It starts with uneasy feelings, followed by fatigue, bouts of exhaustion, and recurrent flu-like symptoms. It escalates, tearing up their insides, literally ripping their internal organs bloody. At this point, black splotches can begin to be seen on their skin, spreading the more sin is committed. Soon, they will descend into madness and be overcome, becoming demons. Once they have become demons, they can never again be cured and will never be an angel. If they die, their energy will be lost, not returned and reformed into new angel ever again.
The only cure that can be found for corruption is found in the same place an angel is born, at the hearth. An angel can come on their own or be brought to the hearth, but they must return there in some way. Once there, they can begin to be cured, but it is far from pleasant. An Arc Angel is needed, one at the very least but most often more. They must place the angel at the center of the Hearth, taking up positions around the platform and using their energy to activate and fuel the Hearth’s task. Then, they will “burn off the sin.”
An intense, white light bursts forth from the Hearth and engulfs the angel, filling every fiber of their being with searing pain. It is a sort of pain that is unimaginable to humans, for they would never survive. Every fiber of their being and every ounce of energy they have is filled with the burning, righteous light of the hearth, which eliminates everything but pure essence of the angel. The more corrupted they were, the longer it will take. For the smallest slight, it may be just a flash but, for those who have been severely corrupted, it can takes weeks. The longest burning in angel history was of an Arc Angel, which lasted for three and a half months. However, lower class angels have never come even near that.
After a burning, angels will remember every deed, every sin, every moment of corruption, but they will be cleansed. The corruption will have been purged from their bodies. There is often a time of rest and reflection, in which the angel is commanded to stay away from any duties and to contemplate, repenting of what got them to that state and recommitting themselves to the right path.
Note: In order for an angel to be purified, at least one arc angel must be present to put their essence and power into the hearth. It's not that their power is what fuels the hearth, more like it's a key that unlocks it. Unlike forging, there's no difference in speed with other angels being there. However, if an extremely powerful angel is in the hearth to be purified or if the angel is overly corrupted, more may be needed to stabilize it so that the angel can't break out in their struggle.
[[Note: The only Arc Angel that ever became fully corrupted was Lucifer, who became an incredibly powerful demon.]]