Originally Posted by Contra_Mundum

Cain said, in essence, "God ought to accept from the labor of my hands that which I deem worthwhile." The contrasts with Abel's offerings are more than superficial. Beside being an atoning sacrifice, Abel's is "of the fat" or best; nothing at all is said about the quality or first-fruit of Cain's, which was not bloody (a requirement that is simply fundamental). Even assuming God was in the habit of receiving "peace" offerings of grain at this time (and there is no indicator that he had authorized them), Cain is clearly not at peace with God, for his "offering" is rejected.