What did Kayin mean when he declared "Gadol Avoni mi'Neso"?
Rashi: This was not a statement, but a question - 'If You can bear the upper realms and lower realms, why can You not bear my sin?' 1
Targum Yonasan: He meant that his rebellion was too large to bear, yet Hashem was able to bear it!'
Ramban: Kayin was confessing his sin. 2 "True", he was saying, "my sin is beyond forgiveness, but You in Your mercy, punished me severely, but not with the death-penalty. Yet the punishment 'Na va'Nad Tih'yeh ba'Aretz,' which leaves me no possibility of building a home for myself, or a pen for my sheep, renders me at the mercy of all who find me, and will inevitably lead to my death!"
Seforno: Now that Kayin discovered that Hashem knows everything, 3 He also knew that his Teshuvah was based on fear of punishment, and was not sufficient to atone for the sin. 4
Sha'arei Teshuvah (4:1): After Teshuvah, he was exempted from death, but he still needed great afflictions.
Oznayim la'Torah: He meant that the punishment of "Na va'Nad Tih'yeh ba'Aretz" was too great to bear, because, as a fugitive who is always on the move, his life would be in constant danger - as he goes on to explain.
Sanhedrin 101b: He actually questioned Hashem - as to why his sin was worse than that of the six hundred thousand of Yisrael (in the desert), whom He is destined to pardon; so why can He not also pardon his sin. 5
Yerushalmi Pe'ah, 1:1: He meant that murder is one of the sins for which man is punished in this world, but the main punishment is reserved for the world to come. 6
Mishnas R. Aharon (Vol. 1 p. 20, Hagahah): Indeed, this is true! It is harder to bear a sin than to bear all the worlds. Great Chesed is needed for a sinner to receive his needs. Therefore, he is far from reward in the world to come.
It is not clear whetherTargum Onkelos interprets the Pasuk ike this or like Targum Yonasan in the previous answer.
Mishnas R. Aharon (Vol. 1 p. 173): After the sin he was very afraid, just at the time of sin he had a spirit of lunacy. This was the level of the early Resha'im!
See Torah Temimah, note 16, citing the Midrash Rabah.
It is not clear as to why it is not then listed in the Mishnah of 'Eilu Devarim', which we recite every morning in Shacharis?
What is the significance of the fact that Kayin refers here to the sin of as "Gadol", whereas the Pasuk in Tehilim 12:4 refers to Lashon ha'Ra as "Lashon Medaberes Gedolos"?
Arachin 15b: It teaches us that Lashon ha'Ra is as bad, or even worse, than murder. 1
See Torah Temimah, note 17, who cites the Gemara that the Torah also writes "Gadol" in connection with adultery and idolatry, and he elaborates.
QUESTIONS ON RASHI
Rashi writes: "'Gadol Avoni mi'Neso' - Is my sin too great to bear?" [Kayin asked] in astonishment." Why does Rashi interpret this way; perhaps Kayin was confessing his sin?
Gur Aryeh: If Kayin was admitting his guilt, he would not have added the word "mi'Neso," which would mean, 'my sin is too great [for You] to bear (i.e. forgive).' Rather, Kayin is asking Hashem rhetorically, 'Surely You are able to pardon my sin.'
