"The atonement of Jesus Christ is the only remedy and rest for my soul."
It seems appropriately morbid on Halloween to explore Martin Van Buren’s purported last words, which an online search shows were “The atonement of Jesus Christ is the only remedy and rest for my soul” (or some variation). 
Van Buren may have made such a statement, but if he did, it was not preserved in the extant historical record. So where does it come from?
It appears to have originated with Kansas City minister Stephen Abbott Northrup. In his 1902 book, A Cloud of Witnesses. The Greatest Men in the World for Christ and the Book, Northrup attempted to refute the argument “that our great thinkers and representative men are not in open sympathy with the religion of the Bible; that Christianity is only for the weak, the young, and the ignorant; and that its champions outside the pulpit, the Christian press, and theological circles are few and far between.” Instead, he argued, it was clear that “master minds in the first rank of statesmanship and scholarship appear in evidence that the very reverse is true: that the wisest, the bravest, and the profoundest are the stanch friends of the Cross and the Word.”
Northrup promised readers that the testimonies he had compiled “have been obtained during years of painstaking research in city, national, and university libraries, and by an extensive correspondence with distinguished men of two continents up to the present hour. The references that follow, or precede, are of indisputable authority, so that those who wish to quote or investigate may feel perfectly assured of their accuracy. . . . The original letters are in possession of the undersigned—deposited under lock and key for safe-keeping, or any possible appeal.”
Included in Northrup’s compilation was the “confession” Van Buren allegedly made “during his last illness”: “The atonement of Jesus Christ is the only remedy and rest for my soul” (pg. 473).
It is less than certain that Van Buren said what Northrup attributed to him, but there is a contemporary account of Van Buren’s supposed final words that may be the germ of Northrup’s quotation. At Van Buren’s funeral, Rev. Benjamin R. Berry reported that one of the former president’s last statements was, “There is but one reliance.” Some newspapers expanded upon these words: “There is but one reliance, and that is upon Christ, the free mediator for us all.” (See, for example, Washington [DC] Evening Star, 31 July 1862, pg. 1.) Could these newspaper reports be the sources Northrup relied on? Perhaps.
If you examine the purported final words of famous nineteenth-century people, what you discover is that they supposedly said a lot of inspiring or memorable things that often seem too incredulous to believe.  A scholarly examination of the accounts of these famous final words seems like a book just waiting to be written.
1. These words are also frequently attributed to Van Buren as proof of his Christian faith, which is a topic for another day.
2. My thanks to Sarah J. Purcell (Grinnell College) for recommending on this point the following article: Marvin P. Rozear and Joseph C. Greenfield, Jr., “‘Let Us Cross over the River’: The Final Illness of Stonewall Jackson,” Virginia Magazine of History and Biography 103, no. 1 (1995): 2–46. Stephanie K. Lawton (Univ. of Virginia) also noted the accounts of Andrew Jackson’s final words, examined in Robert V. Remini, “The Final Days and Hours in the Life of General Andrew Jackson.” Tennessee Historical Quarterly 39, no. 2 (1980): 167–77.