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This is going to be a bit wide of the mark, I fear--not really a commentary on the verses at hand. But the thing has been pressing one me for some time, and this passage from Genesis 4 (which continues for another 7 verses in the first reading for today) calls it immediately to mind. That is, we don't usually interpret this tragic episode in relation to what precedes it in Genesis 3. Yes, it's the beginning of sin, and it's amazing how quickly a little stolen fruit leads to fratricide. But it also--I believe--should be read in light of Genesis 3: 16.
however, hear about this tragedy. Having two sons myself, I can't imagine anything much worse than one of them murdering the other in cold blood. The pain of childbearing is increased in a fallen world: we go wrong, and badly wrong.