What does Thoreau talk about in the conclusion to Walden?
Thoreau brings up all circumstances of men. He encourages his readers to not necessarily compare their own life conditions to other men, but to value the circumstances they have themselves for the features of what can be learned from them.
However mean your life is, meet it and live it; do not shun it and call it hard names.
I feel at times as if he is simply referring to a similar adage that our society sometimes notes today: "Don't worry, be happy."
He encourages man to consider what one's current situation has to offer and think to make the most of it. He encourages the common man to think, who knows what lies ahead?
Thoreau's Conclusion to Walden is specifically optimistic after having his period of reflection. This period leaves room for him to consider that others might benefit from such experiences.
I would encourage you to read the last paragraph again. Often an author saves a nugget of strong truth for that last paragraph.