וַיֹּ֥אמֶר קַ֖יִן אֶל־יְהוָ֑ה גָּד֥וֹל עֲוֺנִ֖י מִנְּשֹֽׂא׃
— [Неужели столь] велика моя вина, что не снести [ее]? — сказал Каин Господу. —
Rashi
גדול עוני מנשוא MY PUNISHMENT IS GREATER THAN I CAN BEAR (literally, my sin is greater than what can be borne) — This is a question: You bear the worlds above and below. and is it impossible for You to bear my sin? (Genesis Rabbah 22:11).
Chizkuni
גדול עוני מנשוא, “my sin is too great to bear.” Kayin refers to the punishment decreed as a result of his sin. It is more than he thinks he can bear. Having been expelled from having a permanent home on earth is already enough, in his opinion. We find a similar reaction in Lamentations 4,6 where Jeremiah describes the punishment of the Jewish people in similar terms, i.e. ויגדל עון בת עמי מחטאת סדום, “the guilt (and punishment) of my people exceeded that of the people of Sodom;” according to Ibn Ezra, Samuel I 28,10 is also to be understood in that sense. According to another exegesis, Kayin’s exclamation is to be understood as a query? “Is my sin really too great to be forgiven? You have already expelled me from my home etc., and made it impossible for me to plant roots, as the soil will not respond to my labour; my father has been expelled from Gan Eden for his sin, but You have seen fit to let him atone for it. Why do You not give me chance also to atone for my sin?” [Adam is not even on record as admitting having sinned. Ed.]
Ramban
MY SIN IS GREATER THAN I CAN BEAR. This is in the form of a question: “You bear the worlds above and below, and is it impossible for You to bear my sin?” Thus the words of Rashi quoting Bereshith Rabbah.43922:25.
The correct plain interpretation is that it is a confession. Cain said: “It is true that my sin is too great to be forgiven, and Thou art righteous, O Eternal, and upright are Thy judgments440Psalms 119:137. even though You have punished me exceedingly. And now behold, Thou hast driven me out this day from the face of the land441Verse 14. for in being a fugitive and a wanderer unable to stay in one place, behold, I am driven from the land and there is no place where I can find rest. And from Thy face shall I be hid441Verse 14. whereas I will not be able to stand before You to pray or bring a sacrifice and meal-offering for I was ashamed, yea, even confounded, because I did bear the reproach of my youth.442Jeremiah 31:19. But what shall I do? Whosoever findeth me shall slay me,441Verse 14. and You in Your manifold loving-kindness did not decree death upon me.” The sense of this is that Cain said before G-d: “Behold, my sin is great, and You have punished me exceedingly, but guard me that I should not be punished more than You have decreed upon me for by being a fugitive and wanderer and unable to build myself a house and fences at any place, the beasts will kill me for your shadow has departed from me.”443See Numbers 14:9 and Ramban there. Thus Cain confessed that man is impotent to save himself by his own strength but only by the watchfulness of the Supreme One upon him.
The correct plain interpretation is that it is a confession. Cain said: “It is true that my sin is too great to be forgiven, and Thou art righteous, O Eternal, and upright are Thy judgments440Psalms 119:137. even though You have punished me exceedingly. And now behold, Thou hast driven me out this day from the face of the land441Verse 14. for in being a fugitive and a wanderer unable to stay in one place, behold, I am driven from the land and there is no place where I can find rest. And from Thy face shall I be hid441Verse 14. whereas I will not be able to stand before You to pray or bring a sacrifice and meal-offering for I was ashamed, yea, even confounded, because I did bear the reproach of my youth.442Jeremiah 31:19. But what shall I do? Whosoever findeth me shall slay me,441Verse 14. and You in Your manifold loving-kindness did not decree death upon me.” The sense of this is that Cain said before G-d: “Behold, my sin is great, and You have punished me exceedingly, but guard me that I should not be punished more than You have decreed upon me for by being a fugitive and wanderer and unable to build myself a house and fences at any place, the beasts will kill me for your shadow has departed from me.”443See Numbers 14:9 and Ramban there. Thus Cain confessed that man is impotent to save himself by his own strength but only by the watchfulness of the Supreme One upon him.