There are many similarities between the sin of Adam and Eve in the Garden of Eden, and Cain’s murder of Abel.
The textual parallels between the two are more numerous than I can list here. In short, the closeness in linguistic style places these sins in tandem as the first two transgressions of human history. But here begins our question for discussion: Adam and Eve were EXPLICITLY instructed not to eat from the tree. In contrast, murder or fratricide had not been explicitly outlawed! Humanity was never directly warned against taking another human life. Why then was Cain culpable for this crime? (After the Flood, God sees the need to state the crime of murder explicitly – see Gen 9:5-6.)
The answer would seem to be this: As the Ramban writes regarding the theft and violence of the Flood generation: “It is in intuitive crime and there is no need for it to be explicitly instructed”(6:13). The sin of the Garden of Eden contravenes a direct ban by God. It was motivated by curiosity, desire, temptation, but in its essence, it was a direct affront to God’s law, and as such it stands as the prototype of a religious sin. The sin of Cain is a different paradigm. Although it was driven by jealousy, insult and rage, It is the model of the moral sin. It seems that Cain did not need to be informed that murder was immoral; he knew it! The proof is that he tried to cover up his crime! He was fully aware that he had committed a dreadful violation.
Prof Yonatan Grossman puts it in the following way: “The sin of Adam is the archetype of religious sin (based on an explicit divine command), whereas the sin of Cain is the archetype of the moral sin, murder. By comparing these two sins, the Torah emphasizes the innovation of Judaism – ethical sin is equal to a religious sin! Not only a religious transgression injures one’s relationship with God, but also a failure to treat one’s fellow with morality and goodness.” So please discuss: How did Cain know that murder was wrong? Are moral values innate? Is there a universal understanding that murder is wrong? Where does that come from? Are there other values that are inherent to the human condition? Why does the Torah make the assumption that the villainy of acts such as murder (Cain), theft and violence (the Flood) are self-evident to humanity?