While you don't need to study history, you should definitely read the Wikipedia article on Napoleon's invasion of Russia before starting War and Peace. Not even from an intellectual standpoint, but to just so you're not taken out of the book every other sentence by another reference to a figure or event.
Almost every book has interesting reference that the reader can choose to follow up on. I'm reading a mystery set in the 30s and took a happy diversion into colonial British officers.
I'm a science fiction fan and I like to approach books as though they were set in Jupiter in the far future. One of my beliefs is that great literature transcends the time and place of where it was written. I haven't been disappointed yet.
I'd chalk up some of that to bad/archaic translations. An overwrought translation can easily transform a page-turner into a slog.
It's always worth researching translations to make sure you find the best, most readable one before embarking on a non-English classic.
One of my mantras as a reader is that I no longer am in school and no one is going to make me write a paper or discuss overriding themes. I can read the way I like and enjoy what I like and if I missed all the mustard seed references than it doesn't matter to me.
I could go into a side discussion on how literature is taught but I'm sympathetic to English curriculum developers who have to give students some books to read and have some criteria by which they can make sure students have read and understood it.