Despite the incomprehensible vastness of Other Life, there was no synagogue. And despite [Sam's] profound reluctance ever to step foot in an actual synagogue, there had to be a synagogue. He didn’t long for one, he needed one: you can’t destroy what doesn’t exist.”
-- Narration (Part 1, Section 1)

Importance: This quote introduces a key aspect of Other Life (its size); the fact that it is missing a key, defining element of Sam's real life (the synagogue, with everything about being Jewish that it represents); and the relationship between Sam and the idea of a synagogue (which he shares with his father, the rest of the family, and arguably the novel). The quote also introduces a key element of Sam's character: his drive to destroy that which he creates because it is imperfect. Finally, the quote foreshadows the various examples of destruction (including the "destruction" of Israel) that appear throughout the narrative.

I...
-- Narration (Part 1, Section 1)