Ok here are my 2 pennies worth
I checked a couple different Bible translations and nowhere does it mention that Abels firstlings were BURNT, just that there were "fattened" giving the impression that they were at their peakness. I assume you did what I did when reading this question. I pictured the My Book of Bible Stories illustration
Cain and Abel and their offerings:
Gen 4 spans an unnumbered amount of time from birth of boys to Noah. I think that God had already communicated with Adam about their relationship (the big screw-up and Satan) and that these offerings were mostlikely as attonements which we later see in the likes of Leviticus. Remember now, no where in the Bible does it say Adam will not receive forgiveness (at least I haven't seen it). It holds Adam accountable ultimately more so then Eve (1Tim 2:14) but not a permanent condemnation of either. Sure the WTBS uses the verse about "manslayer" but their past/ current medical jibberish is equal to manslaying too. Anywho.....back to the subject at hand. So since we see that there is an offering, Cain does some produce and Abel some firstlings. (If Adam and company didn't eat meat then certainly they would have to have clothing and hides are faster then looms) We have to assume that a commandment to do so was ordered as God is apparently still friendly with the humans. It goes on to say that God and Cain chat about his favoring Abels offering, God tells Cain if you turn to doing good, there to will be exaltation. So it seems that Cain is having some issues of attitude that are not elaborated.
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