All that God has created is good. Therefore, evil is not a created thing, but a deprivation within what is created. Sin is a moral deprivation. Those who choose to sin act contrary to the goodness in their own nature. For no matter how much a created person sins, their nature as created by God remains good. And so their own nature stands as a witness against them, that they had a good nature from God, yet they willingly and knowingly chose to offend Him by moral deprivation, by sin.
He who loves iniquity, hates his own soul. (Psalm 10:6). A venial sin is not the love of iniquity, for the person remains ordered toward God and all that is good. But a mortal sin turns the person away from God and goodness, and deprives the soul of the state of grace. He who commits mortal sin is contradicting, in a very full way, the goodness of their own soul. And so, figuratively, anyone who loves sin, hates his own soul. (Both the love of iniquity and the hatred of the soul are figures.)
The fallen angels have a good angelic nature, created by God. So their nature stands as a witness against them, though they were given a good nature by God, they chose to contradict the goodness of that nature by grave sin.
And in Hell, the devils and reprobate souls retain the goodness of their natures, such that their good natures stand forever as a witness against them.
Ronald L. Conte Jr.