Comment: The lesson was that Cain did

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In reply to comment: I skimmed quite a lot of it. (see in situ)

The lesson was that Cain did

The lesson was that Cain did wrong to kill his brother for having greater favor, a story against envy and hatred between brothers, the fighting over status and power and all the other lessons that can be plausible drawn from the story.

I don't think we're talking about the same book Ecclesiastes, I've read it many times, nothing you're saying seems to reference it.