Genesis 4:13: וַיֹּאמֶר קַיִן אֶל־יְהוָה גָּדוֹל עֲוֹנִי מִנְּשֹׂא –Cain said to the LORD, “My punishment is greater than I can bear!”
This statement is a direct response to the punishment God had just given him! It doesn’t occur to him that he is deserving of death! Instead, he complains about losing his livelihood and having to wander. Ultimately Cain builds a city rather than accepting his punishment in defiance of God’s judgment. Like his father Adam, Cain refuses to take responsibility for his actions. Someone else is always to blame; whether it was God or his brother, he is not responsible. There is a fair consensus among the commentators who think that Cain does not express contrition over what he did; Cain worries only about the severity of his retribution.
However, an older rabbinic interpretive tradition suggests that Cain is well aware of the enormity of his sin and realizes there was nothing he could do to ever be forgiven. Cain cannot escape the memories of murdering his brother in cold blood.
One Midrashic text adds a most remarkable subtext to the dialogue that took place between Adam and Cain after the death of Abel. Adam wishes to know what transpired between Cain and God. Cain tells his father: “‘I repented and am reconciled,’ replied he. Suddenly Adam began beating his face, crying, ‘How awesome is the power of repentance, and I did not know! Then he [Adam] arose and exclaimed, ‘A Psalm, a song for the Sabbath day: It is a good thing to make confession unto the LORD’ (Ps. 92:2-3).”