Genesis Rabba 22:6
God acknowledged Abel and his offering - was satisfied with it
But did not acknowledge Cain and his offering - was dissatisfied with it
Cain became very angry and his face fell - became like fire
And God said to Cain..if you do well, lifting… - a blessing, as it is written (Lev 9) and Aaron raised his hands to the people and blessed them
And if you do not do well - also refers to lifting, a curse as is written (Lev 22) and they will incur (lit., lift) iniquity
Rashi Genesis 4:7
at the entrance sin is lying - At the entrance of your grave, your sin is preserved.
and to you is it’s longing - of sin, i.e., the evil inclination, which constantly longs and lusts to cause you to stumble.
but you can rule over it - If you wish, you will overpower it.
Ibn Ezra Genesis 4:7
hold high - Many commentators understand this to refer to "your guilt", meaning to bear the consequences. But I believe that it refers to "face, head", since earlier it was written "his face fell", indicating shame, as in the phrase "how shall I hold my head high" (II Sam 2:22). Thus its meaning is: If you do well, you will be able to be proud, similarly to "Then, free of blemish, you will hold your head high" (Job 11:15)
sin crouches - Some say that the word "sin" here is instead of "punishment". Others explain: at your graveside your sins will crouch on the judgment day; these explain the vav in "his urge" as referring to Abel. Thus the reference in "why are you angry?" is: that I accepted Abel`s offering, because he obeyed you, so you are like his master. Others say it refers to the evil inclination, but this is not written. These explain: By the door of your house your sin crouches and accompanies you. And others say it is the opening of the mouth, as in "guard the opening of your mouth" (Micah 7:5). But I believe that the word "sin" refers to human instinct, which crouches within him.
Ramban Genesis 4:7
If you do well, elevation - Most refer this to "your sin"; Ibn Ezra explains it as "hold high your face", as opposed to "why has your face fallen", because the shamed lower their faces and "the light of my face will not fall" (Job 29:24), so that when one respects someone, it is as if he holds high his face. And this is the meaning of "perhaps he will hold my face high" (Job 32:21) and "you shall not hold high the face of the poor" (Lev 19:15); but I believe it means: if you do well you will outshine your brother, since you are the older. This is the meaning of "why are you angry?" - because when he was ashamed because of his brother, his status fell and when he became envious of him, he killed him. God said to him "why are you angry" - at your brother - and "why is your face fallen," because of him; "if you do well" you will outshine your brother, "but if you do not do well" - evil will not only come to you from him, "but by the door of your house your sin crouches - to foil you in all you do. "And its urge is toward you" - it will desire to cling to you always, but "you will rule over it" - if you want, you will improve your ways and get him off your back. Thus God instructed him on repentance, that he was capable of repenting any time he wanted and He would forgive him.
Targum Jonathan Genesis 4:8
Cain said to Abel his brother, "Come, let the two of us go out to the field." And when the two of them went out to the field, Cain spoke up saying, "I perceive that the world was created on the basis of Mercy, but it is not conducted in accordance with the quality of one`s deeds and justice is prejudicial - why was your sacrifice accepted and mine wasn`t?" Abel answered him saying, "The world was indeed created on the basis of Mercy, and it is conducted in accordance with the quality of one`s deeds and justice is not prejudicial - because my deeds were better than yours, my sacrifice was accepted." Cain responded, "There is no justice and there is no judge; there is no world to come and the righteous are not rewarded nor the evil punished." Abel said, "There is justice and there is a judge; there is a world to come and the righteous are rewarded and the evil punished." Out of these words, they began to fight in the field. And Cain pounced on Abel and sank a stone into his forehead and killed him.
Genesis Rabba 22:7
And Cain said to Abel his brother - About what did they quarrel? `Come,` they said, `let us divide the world. One took the realty and the other the movables. The former said, `The land you stand on is mine,` while the latter said, `What you are wearing is mine.` One said, "Strip`; the other retorted, `Fly.` Because of this quarrel, Cain rose up against his brother Abel…
Rabbi Joshua of Siknin said in R. Levi`s name: Both took realty and both took movables, but about what did they quarrel? One said "The Temple must be built in my area,` while the other claimed, `It must be built in mine.` For thus it is written, "And when they were in the field" - "field" is nothing other than the Temple, as you read "Zion shall be plowed as a field" (Micah 3:12). Because of this argument, Cain rose up against his brother Abel…
Judah b. Ami said, `Their quarrel was about the first Eve.` Said R. Aibu, `The first Eve had already returned to dust.` Then what was their quarrel about? Said R. Huna, `An additional twin was born with Abel, and each claimed her. The one claimed, `I will have her, because I am the firstborn.` And the other said, `I will have her, because she was born with me.`
Genesis Rabba 22:8
And Cain rose up against his brother Abel…R. Johanan said, `Abel was stronger than Cain, for the expression `rose up` can only mean that he [Cain] lay beneath him. He [Cain] said to him, `We are the only two in the world: what will you tell our father [if you kill me]?` At this he was filled with pity for him; immediately he rose up against him and killed him.
With what did he kill him? R. Simeon said, `He killed him with a staff, since `and a young man for my bruising` (Gen 4:23) implies a weapon which causes a bruise. And the Rabbis said, `He killed him with a stone,` since `for I have killed a man for wounding me,` designates a weapon which inflicts wounds. R. Azariah and R. Jonathan in R. Isaac`s name said, `Cain watched closely where his father butchered the bull, as is written, `It shall please the Lord more than a bull` (Ps 69:32), and there he killed him, by the throat and its organs.`
Rashi Genesis 4:8
And Cain said - He entered with him into words of quarrel and contention, to find a pretext to kill him. There are Aggadic interpretations on this matter, but this is the plain meaning of the verse.
Ibn Ezra Genesis 4:8
And Cain said - Most likely he told him all that God had admonished him. And there are sophists born on a cold day who ask how he could have killed him without a sword? This is an absurd question - he could have killed him by choking him with his hands, or with the thousands of sticks and stones that were available.
Ramban Genesis 4:8
And the meaning of And Cain said to his brother Abel - He entered with him into words of quarrel and contention, to find a pretext to kill him, in Rashi`s words. And Ibn Ezra said that most likely he told him all that God had admonished him.. But I believe that these words are connected with the words "when they were in the field," because he said to him "let us go out into the field" and he killed him there in secret. Perhaps he intended that by killing him, the world would descend from him, since he thought that his father couldn`t have any more children, and he also feared lest the major part of the world [humanity] descend from his brother, since his offering had been accepted;
And Cain arose. Without prior conflict, similarly to "he ambushes him and pounces on him" (Deut 19:11).
Rabbi Isaac said: Come and see. When Cain killed Abel, he didn`t know how the soul leaves the body, so he bit him with his teeth, like a viper.
Genesis Rabba 22:11
And Cain said to the Lord: My iniquity is too great to bear - You bear the upper and lower worlds, yet can you not bear my crime?
Is my iniquity too great to bear - This is a question. You bear the upper and the lower worlds, yet can you not bear my crime?
My punishment is too great to bear - All the commentators agree that he admitted his sin and that the meaning of "bear" is similar to "forgive", as in the phrase "forgiving iniquity" (Exod 34:7). But in my opinion, Hebrew refers to the result as "reward" and the punishment that comes as a result of iniquity is called "sin". Similarly, "for the punishment of the Amorites is not yet complete", or "no punishment will be exacted on you" or "the punishment of the daughter of my people is greater". The meaning therefore is that this punishment is too great, I cannot bear it - and the correctness of this interpretation is borne out by the continuation.
Ramban Genesis 4:13
My iniquity is too great to bear - This is a question. "You bear the upper worlds and the lower worlds, and my iniquity is impossible for You to bear?" in Rashi`s words, from Genesis Rabba 22:11; But the correct meaning of the peshat is aconfession - he said, it is true that my sin is too great to be forgiven, and you Lord are righteous and your judgments are correct, although you have punished me severely "surely you have banished me this day from the face of the ground. Because as a vagabond and a wanderer, I will never be able to settle in one place, I am banished from the land and have nowhere to rest, and I am excluded from your presence, because I cannot stand before you to pray or make sacrifices or offerings, for I am ashamed and disgraced, for I bear the shame of my youth. But what will I do if anyone who finds me can kill me, and you in your great grace have not condemned me to death. So the matter is that he said to God "Behold my sin is great and you have punished me severely, but protect me so that I not be punished more than you designated; because I will be a vagabond and a wanderer and I will not build a home and fences anywhere, animals will kill me, since you no longer protect me." He admitted, then, that man is not exalted and able to flee on his own, but only with the help of his Superior.
Midrash Tanhuma (Warsaw) Genesis, Ch. 9 -10
In the course of time, Cain brought, etc. – "the course of time" can mean one year, two years, days and 40 years. The sages say: Cain and Abel were 40 years old.
Cain brought of the fruit of the ground
– What is meant by this? He brought the leftovers of his food. And the Sages said, It was flax seed.
While Abel brought firstlings from his sheep and their fatty parts – In accordance, mixture of wool and flax is forbidden, as it is written (Deut 22) You shall not wear shatnez….
And the Holy One, Blessed be He, said: It is unbecoming that the offering of a sinner be combined with the offering of a virtuous man. Hence it has been forbidden.
Cain said to Abel his brother – What did he say to him?
Let us divide the world between us, and as eldest, I will take a double portion.
Abel said to him: A deal.
Cain said to him: In that case, I will take, in addition to my own portion, the place in which your offering was accepted.
Said Abel: No you won`t. And over this began their quarrel,
as it is said: As they were in/on the field. And below it is written (Micah 3):
Zion will be ploughed like a field.
And some say that Cain said to Abel: Let us divide up the world.
And he said: Yes.
Abel took his flocks and Cain his land to till and they stipulated that this would be a quit claim. But after Abel took his flock he began to graze them (on Cain`s land) and Cain began chasing him/them from hill to valley and from valley to hill, until they grabbed one another. Abel was overpowering Cain, who fell beneath him.
When Cain saw this, he began to plead: Abel, my brother, do me no harm.out of pity, (Abel) freed him, but when he stood up, he killed him, as it is said: And Cain arose – from having fallen.
After killing him, he thought: I will flee from my father and mother, who will ask only me about him, since there is no one else in the world. At once, the Holy One, Blessed be He appeared to him and said: You can flee from your parents, but not from Me.