Aware that he was dying of tuberculosis, Thoreau cut short his travels and returned to Concord, where he prepared some of his journals for publication. Although he never earned a substantial living by his writings, his works fill 20 volumes.

Thoreau died of tuberculosis on May 6, 1862, at the age of 44. He is buried on Authors' Ridge in Sleepy Hollow Cemetery in Concord, Massachusetts. Thoreau was a man full of dreams and ideals, writing about nature and philosophy of life. He spoke out on many social issues such as peace, living simply, abolishing slavery, and was a vigorous advocate of civil liberties. He is regarded as one of America's most influential writers.

Though overlooked during his lifetime, he is now acclaimed as one of the most influential voices for the natural environment. His idea-"In Wildness is the preservation of the World"-has helped shape the thinking of modern day environmentalists. Today many people take Thoreau as the father of this century's environmental movement. Thoreau was one of the first environmentalists, and he interpreted nature in a way that hadn't been done before. For Thoreau, nature isn't just a mirror to man's soul, as it was for the Romantics, nor is it celebrated within the confines of a well-ordered landscape or farm, as it is in the pastoral tradition.

Thoreau was an insightful writer full of dreams and ideals, thinking and writing about nature and life. He reflected on lots of social issues such as abolishing slavery, living simply, peace, and was an passionate advocate of civil liberties. He is now respected as one of America's most influential writers.
II. Introduction of Thoreau’s masterpiece, Walden
Walden (first published as Walden; or, Life in the Woods), by noted transcendentalist Henry David Thoreau, is a reflection upon simple living in natural surroundings. The work is part personal declaration of independence, social experiment, voyage of spiritual discovery, satire, and manual for self-reliance. First published in 1854, it details Thoreau's experiences over the course of two years, two months, and two days in a cabin he built near Walden Pond, amidst woodland owned by his friend and mentor Ralph Waldo Emerson, near Concord, Massachusetts. The book compresses the time into a single calendar year and uses passages of four seasons to symbolize human development.
By immersing himself in nature, Thoreau hoped to gain a more objective understanding of society through personal introspection. Simple living and self-sufficiency were Thoreau's other goals, and the whole project was inspired by transcendentalist philosophy, a central theme of the American Romantic Period. As Thoreau made clear in his book, his cabin was not in wilderness but at the edge of town, about two miles (3 km) from his family home. Following are the themes of Walden:

(1) The slumbering of mankind and need for spiritual awakening

To Thoreau, the trappings of nineteenth century existence the cycle of tiring work to support property ownership forced the common man to live as if he were sleep-walking. Thoreau uses the idea of slumbering as a metaphor for mankind's propensity to live by routine, without considering the greater questions and meaning of existence. Therefore, Thoreau urges his readers to seek a spiritual awakening. He emphasizes the perspective he gains by awakening early and experiencing nature while others in the village are still sleeping and using the metaphor of awakening in the morning to demonstrate the difference between himself and his Concord townsmen. The spiritual awakening of Thoreau and his readers is reflected both in the times of day and in the seasons of the year, with the greatest self-awareness and spiritual discoveries occurring in the morning and spring.

(2) Man as part of nature

Living in a society in which man in the form of railroads, factories, and other technical innovations had begun to tame and control nature, Thoreau counters the separation of man from society by conceiving of man as a part of nature. Through his life in the woods, living for the most part off the fruits of the land and deriving intellectual stimulation from plants and animals, Thoreau demonstrates that man can live successfully in the midst of nature. The animals give him companionship and accept him as a familiar part of their environment. Even nature itself is empathetic to him, for example waiting to blow its coldest winds after Thoreau builds his chimney and plasters his walls. The assertion that man is part of nature promotes Thoreau's suggestion that most people who be more intellectually fulfilled and spiritually aware away from the smothering cocoons of city and village life.