The titular protagonist of mother!, and our frame of reference for the entire film, Jennifer Lawrence’s mother is a combination of two figures: Mother Earth, and the Virgin Mary.
As she throws that lighter down into the pool of oil around her feet, Lawrence’s Mother avenges her fallen child, and destroys humanity in an apocalypse.
Darren Aronofsky has laid it on thick about Lawrence playing Mother Earth in the information leading to the film’s release.
This basically informs the ending’s sense that while God can create and forgive, nature is a bit more indiscriminate when it comes to humanity following the rules.