In 1817, at the age of twenty-eight, and two years after graduation, his _alma mater_ recognizing the tendency of his mind towards the exact sciences, as well as the extent of his acquirements, chose him tutor in Mathematics and Natural Philosophy at Harvard. There also, very soon afterwards, chiefly under the instruction of the Rev. Dr. Ware, who was then the Hollis Professor, he commenced the study of divinity, pursuing it zealously during two years, being, at the same time, the "working editor" of the North American Review. Its numbers from May, 1817, to March, 1819, inclusive, were edited by him. In May, of the latter year, at the age of thirty, he was called to Baltimore and ordained in this city as the first pastor of the Unitarian church which had just been erected. On this memorable occasion, the Rev. Dr. William Ellery Channing preached that discourse in exposition of the Unitarian faith, which has been so widely celebrated, published, and read in America and Europe: a discourse which is said to have "caused more remark on its theological views, while more controversy grew out of the statement of doctrines therein declared, than any single religious discourse in this country ever occasioned." As clergyman of this congregation, Mr. Sparks remained a resident of our city for four years. He is well remembered in the families of his own church and of other religious societies, among whose members his firm but genial manners always made the studious and estimable gentleman a welcome guest. He was a steadfast laborer among his congregation; but the ultimate literary drift of his life was already beginning to develop itself, having probably received an impetus from his editorial task on the North American Review. In addition to his clerical duty in Baltimore, he did a great deal of work in editing the Unitarian Miscellany, in publishing his well-known Letters on the Comparative Moral tendency of the Unitarian and Trinitarian Doctrines, which drew on him the controversial notice of that renowned champion, Dr. Miller, of Princeton, and produced a discussion, which, instead of estranging the combatants, strengthened their personal relations, and increased their mutual confidence and respect. In after years, when Mr. Sparks required a Life of Jonathan Edwards for his American Biography, he selected Dr. Miller to write it, and, in the truly liberal spirit that always governed his editorial labors, and, indeed, his whole literary life, published the memoir of the great Calvanist "without the alteration of a single word." It was here, too, in Baltimore, in consequence of a sermon against Unitarianism by the late Rev. Dr. Wm. E. Wyatt, of St. Paul's, that Mr. Sparks published his volume of Letters on the Ministry, Ritual, and Doctrines of the Protestant Episcopal Church. It was in Baltimore, in 1822, that he arranged and began the republication of Essays and Tracts in Theology by Wm. Penn, Bishop Hoadley, Newton, Whitby, Evelyn, Locke, and others.