Kommentar zu Bereschit 4:24

כי שבעתים יקם קין IF CAIN SHALL BE AVENGED SEVENFOLD — (according to Rashi, as previously explained, it signifies “If vengeance shall be taken on Cain after seven generations”). If in the case of Cain who killed with premeditation the punishment was suspended for him until the seventh generation, in the case of myself who slew inadvertently does it not necessarily follow that it should be suspended for me until many seven generations?

ולמך שבעים ושבעה. My anguish over what I have done will be many times greater than the anguish of Kayin who had been condemned to be a constant fugitive on the earth. 'כי שבעתים יוקם קין וגו, for if Kayin’s punishment was indeed great, my punishment for having killed my son will be many times greater. [he referred to the anguish he suffered over what he had done, not to the punishment imposed upon him externally, as retribution. Ed.]

כי שבעתים, this has already been explained in the previous verse. The purpose of the Torah recording all this for all posterity is to demonstrate that in former times, even during the era of idolatry which began with Enosh, people were convinced that G’d supervises the personal fates of His creatures here on earth, meting out punishment to the wicked and reward to the deserving.