One could build an argument that Toni Morrison is connecting Sethe to Seth and his brothers. Sethe’s story seems to encompass bits and pieces of all three brothers. Like Cain, Sethe kills a member of her family and is ostracized for it. Of course, Sethe doesn’t literally die like Abel. However, one can claim that the ordeal with her baby ultimately leaves Sethe in the same place as Abel. As Sethe does not die until the end, she also contains parts of Seth. Similar to Seth, Sethe survives an intra-family murder.
Conversely, it’s possible to contend that the significance has less to do with how Sethe and Seth work together and more to do with how they deviate from one another. In the most literal sense, Sethe is not Seth; she is not a part of his family. This is key because, throughout the novel, Morrison gives clues that Sethe does not practice a normative form of religion.
Early on, Denver thinks she spots her mom praying. She wonders what her mom is praying for. “Not for anything,” Sethe replies. “I don’t pray anymore. I just talk.” With examples like this, it’s possible that Sethe’s name contributes to the idea that she represents an opposition or a disruption to typical Christianity.
By attaching such a biblical name to the main character, Morrison might be toying with the idea that, while it’s perhaps tempting to view Sethe’s struggles in a biblical light, they’re not actually biblical. Sethe’s trauma is not the result of God but of slavery and the people who sustain it.