What is the importance of fire, explosives, and acid in the novel, Thunderhead (Arc of a Scythe)?

Fire, explosives, and acid represent the only remaining natural means of human death. Rowan has honorable intentions to use fire as Scythe Lucifer to eliminate the scythes he views as corrupt. Meanwhile, Purity and her unsavory allies use acid to attempt to end Scythes Curie and Anastasia’s lives. These methods offer both parties the ability to counteract the scythedom and kill people based on their own will.