Returning from the war, Lemuel engaged in agriculture; but he had early been given a pious trend and soon decided to study theology in anticipation of the designs of Providence concerning him. For some time he had been accustomed to read the Bible and sermons of others on the occasions of conducting family prayers in the home of David Rose. From this exercise he mustered sufficient courage to read one of his own sermons, and finally to preach before the local congregations, which marveled at the power of his words. To prepare himself thoroughly to preach, Haynes once planned to attend Dartmouth College, but shrank from it. After studying privately under Daniel Farrand of Canaan, Connecticut, and William Bradford of Wintonbury, Haynes spent a short period teaching a school for whites. He was licensed to preach in the Congregational Church in 1780 and was ordained soon thereafter, beginning his ministry at Middle Granville, where he labored five years. Here Bessie Babbit, a white woman of considerable education and piety, offered him her heart and they were married in 1783. From this small charge Haynes was called to Torrington, Connecticut. A leading citizen was much displeased that the church should have a "nigger minister," and to show his lack of respect for the new incumbent this man went into the church and sat with his hat on. "He had not preached far," said the man, "when I thought I saw the whitest man I ever knew in that pulpit, and I tossed my hat under the pew." Haynes was then called to take charge of the Congregational Church in West Rutland. Here his usefulness was appreciated and his efforts were extended to other towns through his revivals, one of the most successful of which he conducted in Pittsfield. Having developed such power, he was employed, in 1804, by the Connecticut Missionary Society to labor in the destitute sections of Vermont. In 1809 he was appointed to a similar service by the Vermont Missionary Society. In 1814 he preached extensively in Connecticut, appearing before crowded houses, having in his audience on one occasion President Dwight of Yale. With such standing in the church Haynes was expected to manifest interest in the great questions at issue in New England. One of these was the Stoddardian principle of admitting moral persons without credible evidences of grace, to the Lord's Supper, and the half-way covenant by which parents though not admitted to the Lord's Supper were encouraged to offer their children in baptism. In this debate Haynes, with his eloquence and logic, vanquished the famous Hosea Ballou by his powerful sermon based on the text _Ye shall not surely die_. There was also a difference of opinion with respect to the operations of the Holy Spirit, but Haynes stood with Edwards and Whitefield. Being thus active in dispelling clouds of doubt, he brought many back to a more righteous conduct.