The verse in question reads:
Genesis 4:8: “Cain said to his brother Abel; Cain rose up against his brother Abel, and killed him.”
The biblical narrator does not disclose what was actually spoken between the two brothers. Ibn Ezra suggested that Cain spoke to his brother about the words YHWH had said to him. However, one might argue that it is doubtful Cain would have told his brother everything God disclosed to him, namely, the divine reprimand. Abel’s silence is striking. The Jerusalem Targum offers a moving Midrashic paraphrase of the narrative:
And it was when they went out to the field, Cain answered and said to Abel his brother, “There is neither justice nor is the world accountable to an Ultimate Judge, nor is there another world [beyond this one]; neither is there a good reward given to the just, nor will vengeance be exacted of the wicked. Nor was the world created in goodness, nor is the world conducted with goodness. Therefore this is the [real] reason why your sacrifice was accepted with good will, and mine was not accepted with good will [The universe is a capricious reality, and God is indifferent to the welfare of humankind –MS].” Abel replied to Cain, “There is justice, and there is a Judge: there is another world, and a good reward is given to the just, and vengeance taken of the wicked. The world was created with goodness and it is governed with. But ultimately, everything goes according to the quality of the deeds. Because my works were superior to yours, my offering was accepted with good will, and yours was not accepted with good will.” And as they two disputed on the field and Cain arose against Abel his brother, and killed him.
Midrashic interpretation adds a nuance that does not appear in the original biblical story that is suggestive. The absence of brotherly concern and empathy on the part of Abel toward his brother’s failure only made Cain feel more resentful toward his successful brother. Instead of de-hostilizing his angry and resentful brother, Abel’s self-righteous attitude only added more fuel to the fire. Whereas at first Cain felt anger at God, now he directs his anger toward God via his brother, who has now given him an excuse to “even the score.” So long as Abel lived, Cain thought he would live the most marginal kind of existence. Once Abel was dead, Cain thought that his low self-esteem would cease.