In the course of one week – Gaspar died on Monday, Dora on Thursday, his father on Sunday – [Tomas’] heart became undone like a bursting cocoon. Emerging from it came no butterfly but a grey moth that settled on the wall of his soul and stirred no farther.”
-- Narration (Part 1, Section 1)

Importance: This quote sums up the situation of the protagonist of this first part of the book – specifically, the trio of losses that he experienced in a very short time that, in turn, led him to his grief-triggered decision to walk backwards through his life. There is the sense that the description of grief applied here to Tomas’ experience could be seen as applicable to the grief-based experiences of the similarly grief-stricken protagonists of the book’s other parts.

Tomas, I hope you are aware that what you have before your eyes is a highly trained orchestra, and it plays the most lovely symphony...
-- Uncle Martim (Part 1, Section 1)