/lit/ - Literature

Help me I'm a newfag to classic literature and I have a question.

Do you understand everything in a book? Cause when I tried reading Moby Dick and War and Peace (only read the first ch of the two) I could only understand 70-80% of what it's saying and the parts that went over my head is when the author goes on long tangents on politics or a topic that I would only understand if I was born in that era. Tell me, do I have to understand these sections to appreciate the themes the author is presenting, or can I just forget about them and focus on the big picture. Yes, you don't need to tell me I'm retarded I already know. Thanks!