Reread this quotation from near the end of Walden.Many a forenoon have I stolen away, preferring to spend thus the most valued part of the day; for...

When you consider that Thoreau was a transcendentalist,
and could loosely be considered an American "philosopher" you have to address this
question in the terms that here he is speaking metaphorically.  Certainly "I was rich,
if not in money," is key to understanding this quote.

Think
about it.  The entire book is Thoreau's reflection on life, beauty, love, and
purpose/meaning through the context of contemplation on Walden Pond (nature).  Rather
than spending that time inside, in a book, working for a living, educating himself
traditionally in order to perhaps promote a career, or even spending time traditionally
speaking and teaching others, Thoreau was alone, outside, listening
to nature, thinking, and writing.

Two questions to ask
yourself which will help you come up with a personal answer to your teacher's question
are these:

1. Does Thoreau seem to regret the time
   he spent on Walden pond?  Why or why not?


2. Given his
   feelings on the time he spent alone in nature, what do you believe Thoreau would claim
   as the most important things in life?

I think
if you can answer the above questions, you will successfully explain the quote, and it
will your answer, which is exactly what your teacher is looking
for.  Good luck.