Walden is a brilliant book. The quotations you hear from it are pretty clear cut:
"I learned this, at least, by my experiment; that if one advances confidently in the direction of his dreams, and endeavors to live the life which he has imagined, he will meet with a success unexpected in common hours."
"The mass of men lead lives of quiet desperation."
What lies behind us and what lies ahead of us are tiny matters compared to what lives within us.
I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived. I did not wish to live what was not life, living is so dear; nor did I wish to practise resignation, unless it was quite necessary. I wanted to live deep and suck out all the marrow of life, to live so sturdily and Spartan-like as to put to rout all that was not life, to cut a broad swath and shave close, to drive life into a corner, and reduce it to its lowest terms.
If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music he hears, however measured or far away.
Our life is frittered away by detail. Simplify, simplify.
And then people buy the book and find it very hard going. The problem is that Thoreau had a rich classical education, and there are often allusions to Greek or Roman, even Indian mythology. Add the long winded 19th century style and it's tough for the modern reader.
The solution is to get an annotated edition, or use the study notes available on the web (I get the impression Thoreau is taught in US schools, so there are lots of resources available.) Then the opaque references become much clearer.
It's hard work - like friction firelighting. But at the end, if you stick with it, you get light.