One of the dismaying facts about literature, which emerges from studying it, is the extent to which it seems motivated - and is certainly permeated - by vengefulness.
In other words quite a lot of art appears to be motivated by the desire for revenge.
For example, the novels of Saul Bellow seem to be exceptionally motivated by the desire to get-back-at various real life persons. In terms of quality, I would regard Bellow as having one of the finest prose styles of the 20th century - quite intoxicating. But the human motivations driving his books seem exceptionally negative and petty.
As I understand it, the desire for revenge is the opposite of forgiveness, and is therefore completely prohibited - and it does not make any difference to this prohibition whether the vengefulness is open or covert: writing a revenge-motivated Roman a Clef (in which you dissect and demolish disguised versions of ex-wives, nasty bosses and unstrustworthy friends) is prohibited.
The prohibition is especially necessary because it is so enjoyable to indulge in this kind of covert revenge - and at the same time it is completely deniable when done well.
I know. I've done it, and not once. As sins go, it was deliciously enjoyable and (in worldly terms) consequence free to 'get back at' people who had (as I felt) betrayed, oppressed or simply annoyed me. Had I the genius of Bellow and the magnitude of his readership it would no doubt have been vastly more pleasurable.
Which is precisely why vengefulness is so utterly corrupting - and why I cannot get through a Bellow novel these days.