He removed to Salem in the month of June, 1815, where he found many cordial and true friends, whose memory and companionship he cherished to the close of life. While resident here he wrote a pamphlet in reply to one by John Kelley, A. M., entitled "Solemn and Important Reasons against becoming a Universalist." This review was comprised in a pamphlet of eighty pages, and is a strong and powerful argument in favor of the principles which the author believed, and which he advocated with such successful zeal. These minor publications of Mr. Ballou's, when now referred to, convey but a faint idea of the interest which they then produced. Their extended and immediate influence was evident. Vast numbers were sold; some zealous people, rejoicing at the joy unspeakable to which they had themselves attained through the author's writings and public communications from the pulpit, purchased them by wholesale, and distributed them gratis, far and near. His hearers, too, largely increased in numbers, and he was rewarded for his labors by witnessing the rich harvest that he was reaping in his Master's vineyard, and the number of souls he was leading in the paths of truth. While resident in Salem, he also wrote a series of letters in reply to a series addressed to him by Abner Kneeland, inquiring into the authenticity of the Scriptures. The book formed of the letters referred to makes a volume of two hundred and fifty pages. The first edition was published in Salem, in 1816, the second in Boston, in 1820. The origin of these letters, which created no small degree of attention, at that period especially, was as follows: Rev. Mr. Kneeland having at various times expressed serious doubts and fears relative to the genuineness of the holy Scriptures, and the system of Divine revelation therein contained, solicited Mr. Ballou to enter into a correspondence with him upon the subject, in which Mr. Kneeland agreed to do his utmost to disprove the truth and authenticity of the Bible, while Mr. Ballou should take the opposite ground, and as strenuously defend it. It was thought that this mode of discussion would be of mutual benefit to them, and at the time of its commencement was designed solely for their private use. But they were finally published, at the solicitation of friends, and with the hope that they might be productive of more extended good. These letters, which are somewhat lengthy, and indeed necessarily so on the part of Mr. Ballou, who assumed the laboring oar, were always written, as he has told us, at a single sitting. They are highly valuable, and were more particularly so at that period, as forming a powerful chain of evidence in favor of Christianity, and are characterized, on Mr. Ballou's part, by a vigorous accuracy and earnest desire after truth, which prepossesses the reader in their favor.