I had never thought too much about how Cain killed his brother Abel in Genesis 4. Some movies and images depict him picking up a rock or a large bone and hitting him over the head. But I learned something recently that makes it a bit more graphic and gives more insight into what Cain was thinking.
Verses 3 to 6 tell how Cain was mad because God did not accept his sacrifice of “some” of what he had harvested, while accepting the sacrifice that his brother Abel made of his “best” lambs. So Cain invited Abel to go out to the field with him soon after this.
4:8 says “And while they were in the field, Cain attacked his brother Abel and killed him.” He probably took the sharp object used to sacrifice animals, slashed Abel’s throat (jugular), just like Abel did to sacrifice his lambs, and spilled all his blood out on the ground. Jealousy and revenge, possibly thinking, “Now there is a better sacrifice!”
4:10 talks about how much blood was on the ground: “The Lord said, “What have you done? Listen! Your brother’s blood cries out to me from the ground.” The word used for “murder” in 1 John 3:12 recounting what happened is a word signifying killing a lamb for the slaughter.
Another reason to think this may be true: At that time, Adam’s family never killed anything other than the lambs for the sacrifice. Many years later, after the flood, Genesis 9: 2-3 says: “The fear and dread of you will fall upon all the beasts of the earth and all the birds of the air, upon every creature that moves along the ground, and upon all the fish of the sea; they are given into your hands. Everything that lives and moves will be food for you. Just as I gave you the green plants, I now give you everything.”
Many people think, that for the most part, people only ate what grew wild or what they had planted up until the flood, as implied by these verses. So it is very possible that the only “killing” they had experienced were sacrificing the lambs on the altar, slashing the throat. So could it be that Cain killed Abel in the same way? With no experience in killing, would he think to grab a rock or something like that to kill him? It makes more sense, especially based on the way he was thinking, that he killed him in a way he knew would be effective.
After Cain was mad after God accepted Abel’s sacrifice and not his, (“but on Cain and his offering he did not look with favor. So Cain was very angry, and his face was downcast.”) God warns Cain to “guard his heart” saying: “Why are you angry? Why is your face downcast? If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must master it.” (4:6-7)
Cain did not “master” sin. He killed his brother, sacrificed him, upset that God had accepted Abel’s sacrifice and not his, and in his warped thinking blamed Abel. John uses this as an extreme example of how not to love your brother! But Jesus said if we start and keep resentment and bitterness in our hearts against others, it can lead to us acting in some pretty bad ways.