Check out these wonderful lyrics and an explanation.
https://thejesusquestion.org/2012/07/09/the-battle-hymn-of-the-republic-its-origin-and-meaning/
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.