There were two kinds of Forging affinities: mind and matter. Someone with a matter affinity could influence one of the three material states: liquids, solids, or gasses. Both Tristan and Zofia had matter affinities; Zofia’s Forging affinity was for solid matter -mostly metals and crystals - and Tristan had an affinity for liquid matter. Specifically, the liquid present in plants.”
-- Laila (Part I: 2. Laila)

Importance: This establishes the specifics of Forging and allows the audience to understand how it works on a fundamental level. First, it explains what Tristan and Zofia can do and differentiates their own abilities. Second, it clues the audience into the mind affinity that no character has shown at this point in the novel. This means that, when the audience meets Hypnos in the next chapter, his illusion powers make sense. This builds trust between the narrator and the reader, as the audience knows they will be given the information...