I'm reading The Bhagavad-Gita. I read that Thoreau kept a copy of this in his cabin on Walden Pond. I can see why. An excerpt:
The self is the friend of a man
who masters himself through the self,
but for a man without self-mastery,
the self in like an enemy at war.
Knowledge means humility,
sincerity, nonviolence, patience,
honesty, reverence for one's teacher,
purity, stability, self-restraint;
The book stresses self-discipline and action, both, I believe, Thoreau was heavily into.