All the basic parts are there, Heidi, and from the outside she looks like she should work just fine, but inside there are lots of mysterious little pieces busted or bent or missing altogether, and without them her machine doesn't run quite right.
-- Bernadette (Heidi paragraph 2)

Importance: This quote is Bernadette explaining Sophia's mental disability to young Heidi.

That word, soof, became like a little burr sticking in my head, pricking me so I couldn’t forget it was there.
-- Heidi (Soof paragraph 29)

Importance: This is when Heidi becomes obssessive about finding out what "soof" means. This obsession drives her to go on her journey.

It's okay, I won't tell nobody," he said.
-- Zander (Out paragraph 58)

Importance: This is the moment when Heidi gains insight into Zander's inner world. All the judgement she had harbored against him fall away as he becomes humanized in her eyes.

We both know I can't stopy you, don't wek Heidi-Ho?
-- Bernadette (Back Soon paragraph 35)

Importance: This is when Bernadette acknowledges that...