How is the section of Pyramus and Thisbe related to the central theme?

Are you referring to The Metamorphoses by Ovid.

The main theme of the epic poem "Metamorphoses" by the Roman poet Ovid is about the transformation of characters in mythical stories. The poem explores the idea that changes are an inevitable part of life, often brought about by supernatural or divine intervention. One of the most notable sections of the poem is the story of Pyramus and Thisbe, which is related to the central theme of transformation. The tale tells of two young lovers who are prohibited from being together by their parents. They secretly communicate through a crack in a wall between their houses and plan to elope. However, when Thisbe arrives at their meeting place, she sees a lioness with blood on her mouth and runs away in fear, dropping her veil in the process. Later on, Pyramus finds the veil and, thinking Thisbe has been killed by the lioness, kills himself. When Thisbe returns and sees Pyramus dead, she also takes her own life. Their blood stains the white berries of a nearby mulberry tree, turning them red. Although the transformation in this story is not a physical one, it does involve a transformation of the characters' identities. Pyramus and Thisbe begin as hopeful and in love, but their relationship is ultimately thwarted by their parents and leads to their tragic deaths. The tale underscores the idea that powerful emotions, such as love, can result in significant changes and transformations in a person's life.