I was asked to explain this a little bit. It’s a funny thing that Cain’s act seems cynically rather intuitively obvious, (“Well, he was jealous!”) and at the same time blatantly irrational, serving no real or even imagined interest of Cain’s, and not even avenging a perceived slight.
It was God, not Abel, who rejected Cain’s sacrifice, and the mere fact that retaliation against God is impossible really does nothing to undo the absurdity of an act of violence against Abel. Of course every part of this is as familiar as violence itself; we are so used to irrational, self-destructive, downright mindless violence that the most incomprehensibly idiotic acts fit neatly into well-used human categories. We have no reason for what we do, but we have a name for it, and even a narrative cliche for the things we have done a million times, and should not have even been stupid enough to do once.
So to begin with, the reason that Cain killed Abel is that he acted in error. He acted evilly, but not in the sense we often imagine of ruthless self-interest or dogmatic certainty of a some evil principle, but in the blind wrongness of perverse self-destruction or mindless waste. And there’s something to be said about the circumstance in which he errored, because in the background of Cain’s mysterious action is God’s mysterious action that provoked him. God looked with favor upon Abel’s sacrifice, and not Cain’s; we are tempted, for lack of detail, to call this unreasonable on God’s part. However…If Cain and Abel had each submitted an economics paper to Dr. Friedman, and gotten a similar reception, we would know on that basis alone that one paper was in true fact better than the other, even if we were ourselves incapable of comprehending either paper. If God is anything like Friedman, that is, anything like God must be to be God at all, then his judgement is to be trusted.
Very well, Cain’s sacrifice was defective in a real, but unknown way. Where does that get us? Well where it gets Cain is to an explicit lesson from God, a privilege few enjoy and what could have been the key to major personal growth for Cain.
“6 Then the Lord said to Cain, “Why are you angry? Why is your face downcast? 7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must rule over it.”
It’s a teaching opportunity. It’s direct, sound advice from God to Cain personally in his exact circumstance. It’s how to handle rejection and failure. It’s illumination of the nature of sin: The thing that seeks to rule over you, the error that seeks to corrupt your character and has its moment of opportunity when you make a misstep. It’s God’s wisdom for a situation that will come up over and over again through the life of every human being since Cain. It’s God’s plan for turning your misfortunes into strengtheners of character, of using the hard world he gave us as a force to purify our souls of errors. As hungry belly immunizes the man against the temptation of sloth, so the hard knocks of failure in ambition abrade away the rust of complacent pride and give our dreams the polish that only a resilient surface can take. Such is God’s plan for hardship, such is the strategy by which God prevented sin from blooming immediately into an all-consuming flower of self-indulgence and suicide (a flower some aristocracies have, however, more recently succeeded in cultivating). And then we have Cain’s plan:
8 Now Cain said to his brother Abel, “Let’s go out to the field.” While they were in the field, Cain attacked his brother Abel and killed him.
How much of human history, whether of whole societies or whole men, is described in this little answering of God’s instructions? “No thanks God, I’ll just do something blindly idiotic instead,” said Man to his maker. I’ll just harm my brother, and myself, and gain nothing, because I’d rather pursue an error of my own than the wisdom of God. I’ll just funnel a million lives and innumerable gifts into the monstrous whirlpool of pride that was the Great War. I’ll just take God’s Liberty and modify it to create monarchies and slave classes. I’ll just sell my birthright for porridge.
I can’t give a rational explanation for Cain’s crime, because it was a blatantly, purely irrational act. I haven’t the slightest difficulty in believing the story however, because the proper explanation is intuitive: Cain killed Abel because Cain is exactly the same kind of dumbass that i am.