There is purification in punishment.

Atonement, not punishment, is what purifies us, I think. And not the act of having atoned, but the process of atonement in itself. Taking accountability, responsibility, for the harm we do to others is what re-establishes the goodness in our characters. We are what we do, after all.

EDIT: I wrote this before reading further but already Dorian’s actions reveal the necessity of my correction. Some terrible people think that just because they bear the punishment of their wrongdoing, that their sins are cleansed and that they then should be seen as having paid their due. But that is not how it works. Unless there is sincere accountability for the wrongdoing including by self reflection and internal change, it is fruitless. The fact that Dorian thinks that he can just start doing the right things and that will erase the sins of the his past, without any accountability towards them, not even guilt over murdering Basil, is laughable. He has not changed at all. He is still selfish & self serving — earlier he did the things he did for a personal sense of pleasure & hedonism & now he’s doing the things he’s doing (“being good”) to spare himself negative feelings and thoughts. None of this is due to genuine empathy or compassion towards others.