We commonly do not remember that it is, after all, always the first person that is speaking. I should not talk so much about myself if there were anybody else whom I knew as well. Unfortunately, I am confined to this theme by the narrowness of my experience. Moreover, I, on my side, require of every writer, first or last, a simple and sincere account of his own life, and not merely what he has heard of other men's lives; some such account as he would send to his kindred from a distant land; for if he has lived sincerely, it must have been in a distant land to me.
~Henry David Thoreau, Walden

Sometimes it is best to start with what you don't know, and since you are writing about Thoreau at a fairly young age, you probably don't know enough about his tome of writings to overly praise or condemn him; you probably don't get all the complexities and nuances of his arguments in what you have read, so if you decide to attempt a strict literary analysis, you run the risk of sounding uniformed at best and arrogant at worst--but don't let this dissuade you from writing about Thoreau! This doesn't mean you have not had a profound and transformative literary experience; it does not mean that your thoughts, insights, and opinions are not as valid as those of the most seasoned critic. It simply means that a narrative essay--since its genesis is in the undeniable validity of you--is probably your best approach to writing about your experience reading and reflecting on the first chapter of Walden--that maddening treasure trove of pithy wisdom and parables simply called, "Economy--"