A couple sentences into the paragraph, the "I"-voice of the narrator makes this philosophical statement about truth vs. appearances, and the difficulty of drawing true/correct conclusions about people around us:

"But while the imaginations of other people will carry them away to form wrong judgments of our conduct, and to decide on it by slight appearances, one's happiness must in some measure be always at the mercy of chance. "

Never noticed this before - could it be a "thesis statement" for the book? Certainly many imaginations have been carried away, and wrong judgments formed, and decisions based on slight appearances... and our main characters are finding their happiness beyond their control.