It is just fifty years to-day since I preached my first sermon in Bernard Whitman's church in Waltham. I shall keep the anniversary by beginning the sketch of my life, which my friends have thought may be interesting. I have no remarkable events or adventures to record. But I have lived in an important period; have known many eminent men and distinguished women; have seen great changes in social life, in religious opinion, in private morals and public manners. If I can succeed in making a few suggestive pictures, or memory sketches, it may be a gratification to my children and friends, and possibly contribute matter for the future historian of this period.
The end result of Clarke's efforts was an autobiography of over 400 pages (with the help of Edward Everett Hale), describing the ever-changing world of 19th-century America. He relayed his experience with the Transcendentalists — people like Ralph Waldo Emerson and Margaret Fuller. He wrote of his experience with Brook Farm — he bought the land of this failed experiment (never having been a member) and later donated it to President Abraham Lincoln during the Civil War (it became "Camp Andrew"). During that period, the Reverend Clarke preached to the troops training there.
After Clarke's death, Hale recorded that their mutual friend the Transcendentalist Frederic Henry Hedge said: "You do not get a true estimate of Clarke unless you see him as a poet. He approached all subjects from the poetical side... The rest of us have written as if we were philosophers. Clarke always wrote, no matter how dull a subject, as a poet writes." That first sermon that Clarke preached in Waltham used a phrase which Hale said was "the text of his life": "Whatsoever thy hand findeth to do, do it with thy might."