Noach emerged from the line of Adam and Hava's third son Sheit, whereas Kayin’s descendants were eradicated from the face of the earth during the flood. Adam and Chava’s heroic decision to move on, to persist, to retain their optimism and resolve in the face of tragedy, is what ensured the survival of mankind.
After the narrative of Hevel’s murder at the hands of his brother, the Torah in Parashat Bereishit presents a brief genealogical record of the descendants of Kayin, the killer and surviving brother. Thereafter, the Torah lists the descendants of Sheit, another son of Adam and Chava, concluding with the birth of Noach.
One might wonder why the Torah goes through the trouble of listing several generations of Kayin’s descendants. The listing of Sheit’s genealogical line was necessary in order to reach Noach, the protagonist of the subsequent narrative and the man who essentially became the father of all mankind, after the deluge. Kayin’s descendants, however, did not survive the flood, and there thus seems to be little reason to trace this genealogical line.
One simple answer, perhaps, relates to the cultural and industrial developments with which a number of Kayin’s descendants are credited. Kayin himself built a city (4:17), and a number of his descendants are described as making important contributions in areas such as farming, music and metal work (4:20-22). For this reason, perhaps, the Torah reviews the descendants of Kayin, to tell of the gradual process of industrialization and development that mankind underwent during this period.
We might point to another, perhaps more subtle, purpose, as well. The Torah writes that Chava named her third son Sheit because she responded to her birth by proclaiming, “Shat li Elokim zera acheir tachat Hevel’ – “God has given me another offspring, in place of Hevel” (4:25). Sheit was seen as a “replacement” of Hevel. After Hevel’s murder, Adam and Chava responded by begetting another son, by filling the void left by Hevel’s death. Rather than despairing, they continued their work of populating the earth as God had commanded. They could have easily just given up, seeing how quickly and brutally a life can be taken. But instead of allowing this tragic setback to discourage them, they persisted, in the confident hope that their new son would mark the fulfillment of the dreams that were left shattered by Kayin’s bloodshed.
Sure enough, not only did Sheit survive and beget children, but it was he who became the father of all mankind. Noach emerged from the line of Sheit’s descendants, whereas Kayin’s were eradicated from the face of the earth during the flood. Adam and Chava’s heroic decision to move on, to persist, to retain their optimism and resolve in the face of tragedy, is what ensured the survival of mankind. The boy who was described as “taking the place” of Hevel, who embodied the virtues of persistence and perseverance, ultimately begot Noach, the only survivor of the flood, and in this way became the father of all people.
By presenting side-by-side the genealogical lines of Kayin and Sheit, the Torah perhaps emphasizes the point that specifically the latter’s line produced Noach, and thus, by extension, produced all humankind. As opposed to Kayin’s line, which ended with the flood, the line of Sheit, the product of Adam and Chava’s perseverance, continued, and continues even to this day, thereby underscoring the importance of persistence, of never despairing, of working to fulfill our duties despite heartbreaking setbacks.