And here’s a rather longer commentary:
The melody for The Battle Hymn of the Republic has had quite the most varied career in the history of American patriotic song. It came into being as a Southern camp-meeting song early enough to have been included in Henry Ward Beecher’s Plymouth Collection of 1852. With the organization of the 12th Massachusetts Infantry in 1861 two Maine men in the second battalion introduced to camp “Say brothers, will you meet us, On Canaan’s happy shore?” To this melody the glee club of the unit evolved a set of verses half applied to one of their own members, a Scotch John Brown. When these words became the characteristic song of the regiment, the officers tried in vain to have the words applied to Ellsworth, the first Northern commissioned officer who had fallen in the War. Inevitably many new versions were composed on John Brown of Ossawatomie—by H. H. Brownell, Edna Dean Proctor, Charles Sprague Hall, and anonymous writers; and from these developed variants beyond recall. The hymn had become a war ballad of widest popularity; but the ballad was to be rehabilitated as a hymn again. This occurred when Julia Ward Howe, one of a party to visit the Army of the Potomac in December, 1861, was urged by James Freeman Clarke to dignify the chant with adequate words. Her attempt was christened by James T. Fields and appeared in the Atlantic, February, 1862, as The Battle Hymn of the Republic. The marked differences between these three lyrics show how vital is the relation between words and music. The colourless, seven-syllabled, thrice-repeated line, “Say brothers, will you meet us,” is plaintive, if not dreary, in effect. The eleven syllables of “John Brown’ss body lies a-mouldering in the grave,” with their stronger vocal quality and their sinister suggestiveness, have a primitive folk-quality and a martial vigour. The iambic heptameters of “Mine eyes have seen the glory of the coming of the Lord” rise to the elevation of a religious processional.
Source: The Cambridge History of English and American Literature: XXVI. Patriotic Songs and Hymns - § 5. Civil War Songs; Dixie; The Battle Hymn of the Republic
-Tim