Just to get it out of the way, I picked Capital because it’s extremely popular as well as being legendarily difficult to read. You could probably do Origin of Species pretty easily - I think it’s actually pretty accessible - but there’s no reason to read it at this point unless you’re a biology nerd with a fetish for history. Evolutionary biology, fortunately, has advanced significantly in the past couple of centuries. If you actually are interested in Capital (both as an artifact of its time as well as being a brilliant critique of the system that was starting to hit its stride), I recommend David Harvey. Harvey has several video and text based courses on Capital that make the ideas accessible and make sense both in the context in which they were written and for our more modern understanding. A lot of his work is freely available on YouTube and the web. 

But moving on from Marx, you might benefit from a course in literary analysis. Again, it could be an ebook or a video, but it might help to develop a framework for understanding literature around either a specific period (eg early 20th century versus post war writings) or topics or literary movements. What I’m saying is that if you read scholars who studied Walt Whitman in addition to actually reading his writings, I think you would get closer to what I think your goal is.

In any case, I wish you all the luck in the world and hope you make some remarkable discoveries. I’ve taken multi-year sabbaticals where I did little outside of reading, and I always came out of them with far better growth than a decade of work at a desk.