The first passage comes from the first page of Chapter One: "I was fourteen when I was murdered on December 6, 1973." This tells you that Susie is dead, and that she'll be narrating the story despite that; it tells you what is special about the story.
On the last page of the book there is a line: "And my sister, my Lindsey, left me in her memories, where I was meant to be." That's Susie talking about how very long it has taken for her to be treated appropriately by existence, ever since she's been killed. That's how wrong her life was.
In between, the last line of Chapter Twelve: "Like snowflakes," Franny said, "none of them the same and yet each one, from where we stand, exactly like the one before." This sums up the nature of souls and lives from heaven's perspective.