Treatise or not?

The definition given by Merriam-Webster states that a treatise is a systematic exposition or argument in writing including a methodical discussion of the facts and principles involved and conclusions reached. The written work is considered a treatise if all the discussion and events that took place are given and display the conclusions reached.

 Yes, The Grapes of Wrath is a treatise. Jim Casy was a preacher and one day he decided that he was not going to be a preacher anymore because of his lustful ways. The novel lays out all the facts and principles involved and shows how Jim Casy reached his conclusion. While Jim Casy was a preacher,he was so bothered by the sin that he would beat himself up after each encounter he had. "'Why is it that when a fella ought to be just about mule-ass proof against sin, and all full up of Jesus, why is it that's the time a fella gets fingerin' his pants buttons?'" He then begins to lay out his philosophy of not only sin but also virtue. "I says, 'Maybe it ain't a sin. Maybe it's just the way folks is. Maybe we been whippin' the hell out of ourselves for nothin'." "There's just stuff people do. It's all apart of the same thing. And some of the things folks do is nice, and some ain't so nice, but that is as far as any man got a right to say.'" Jim Casy reached his conclusion and decided that preaching was not for him.
I feel Jim Casy should have had a more righteous reason to stop being a preacher. He was controlled by his lust for the women that he would preach. Tom Joad committed a sin by killing a man with a shovel. If Tom Joad would not have killed that man,the man would have killed him. It was in self defense which makes the sin justifiable.