Written in November 1861 by abolitionist poet Julia Ward Howe, this song seems to glimpse the fiery trial ahead:
BATTLE HYMN OF THE REPUBLIC (lyrics)
Mine eyes have seen the glory of the coming of the Lord:
He is trampling out the vintage where the grapes of wrath are stored;
He hath loosed the fateful lightning of His terrible swift sword:
His truth is marching on.
(Chorus)
Glory, glory, hallelujah! [3x]
His truth is marching on.
I have seen Him in the watch-fires of a hundred circling camps,
They have builded Him an altar in the evening dews and damps;
I can read His righteous sentence by the dim and flaring lamps:
His truth is marching on.
(Chorus)
Glory, glory, hallelujah! [3x]
His truth is marching on.
I have read a fiery gospel writ in burnished rows of steel:
“As ye deal with my contemners, so with you my grace shall deal;
Let the Hero, born of woman, crush the serpent with his heel,
his truth is marching on.”
(Chorus)
Glory, glory, hallelujah! [3x]
His truth is marching on.
He has sounded forth the trumpet that shall never call retreat;
He is sifting out the hearts of men before His judgment-seat:
Oh, be swift, my soul, to answer Him! be jubilant, my feet!
Our God is marching on.
(Chorus)
Glory, glory, hallelujah! [3x]
Our God is marching on.
In the beauty of the lilies Christ was born across the sea,
With a glory in His bosom that transfigures you and me:
As He died to make men holy, let us die to make men free,
While God is marching on.
(Chorus)
Glory, glory, hallelujah! [3x]
Our God is marching on.
Julia Ward Howe’s later account of writing these verses:
We were invited, one day, to attend a review of troops at some distance from the town. … We returned to the city very slowly, of necessity, for the troops nearly filled the road. My dear minister was in the carriage with me, as were several other friends. To beguile the rather tedious drive, we sang from time to time snatches of the army songs so popular at that time, concluding, I think, with
“John Brown’s body lies a-mouldering in the ground;
His soul is marching on.”The soldiers seemed to like this, and answered back, “Good for you!” Mr. Clarke said, “Mrs. Howe, why do you not write some good words for that stirring tune?” I replied that I had often wished to do this, but had not as yet found in my mind any leading toward it.
I went to bed that night as usual, and slept, according to my wont, quite soundly. I awoke in the gray of the morning twilight; and as I lay waiting for the dawn, the long lines of the desired poem began to twine themselves in my mind. Having thought out all the stanzas, I said to myself, ‘I must get up and write these verses down, lest I fall asleep again and forget them.’ So, with a sudden effort, I sprang out of bed, and found in the dimness an old stump of a pen which I remembered to have used the day before. I scrawled the verses almost without looking at the paper. …
— Julia Ward Howe, Reminiscences (1819-1899)[p.274-5]
The Hardtacks 
thank you!