Q. How was it that God was able to punish Cain for killing Abel when the Ten Commandments had not yet been given, or even the Seven Noachide Laws? How was Cain to know that murder was not permitted?A. Let’s first talk about Abraham.
Rabbinic tradition says that he kept the Torah even before it was given (Kidd. 4:14) because he had the spiritual instinct to know what God required (Ramban on Gen. 26:5).
In supporting this assertion the Mishnah quotes the verse, “Abraham obeyed my voice and kept My charge, My commandments, My statutes and My Laws” (Gen. 26:5).
In analysing the differences between “charge”, “commandments”, “statutes” and “laws”, Rashi states that “commandments” indicates laws that would have applied even if they were not written in the Torah – i.e. laws that human beings were capable of working out for themselves, like the prohibition of robbery and murder.
So we can take it that Abraham knew that murder was wrong, but did Cain?
Philip Henry wrote, “When anger was in Cain’s heart murder was not far off”. Now surely God knew that human history was only beginning and Cain needed guidance against anger and what it leads to.
The Midrash implies this when it puts into Cain’s mouth the words, “Master of the universe, if I have killed him (Abel), it is You who created the evil inclination. Why did You permit me to kill him? It is You who killed him, for if You had accepted my sacrifice as you accepted Abel’s, I would not have become jealous of him” (Tanchuma, B’reshit).
Yet despite this, it is Cain himself who is unequivocally blamed for the murder. The reason is implied in the sequence of verses in the Biblical text.
Gen. 4:8 reports the killing; the previous verse provides the warning – “If you do well, shall you not be lifted up? If you do not do well, sin couches at the door and it desires you – but you can rule over it” (Gen. 4:7).
Thus Cain knew that human passions were dangerous and had to be controlled.