Sforno on Genesis 4:13/ספורנו על בראשית ד׳:י״ג

1גדול עוני מנשוא, after Kayin finally realised how G’d in Heaven supervises every detail which goes on down on earth, he was convinced that G’d must know that his sole motivation in doing repentance was to escape punishment. Even this type of repentance was wrung from him only after G’d had pressured him to display penitence. He was embittered, and this is what prompted him to exclaim that the severity of his sin was such there was no hope to obtain forgiveness which would protect him against retribution in kind. The matter is similar to Saul’s failure in killing Agag, King of Amalek. Saul had said to Samuel: “I have sinned,” only after Samuel had insisted that he make a confession of having failed to carry out G’d’s instructions. (Samuel I 15,24) Samuel had had to tell Saul that G’d had despised him as a future leader of the Jewish people before he could prevail on Saul to acknowledge his wrongdoing. (Samuel I 15,24)