Jubilee is called "Jubilee" because of the song the "black cloud" of Union soldiers, riding in "dust from [their] horses hooves," sang as they rode to set the slaves of Georgia free.
We don't usually use long quoted passages with eNotes answers, but I think this bit of very true social history of the deep South merits a little liberty regarding quote length.
277 Early one morning, about the week of May. Vyry was in the kitchen cooking when all the children came running to alarm the house. They could hear a noise like thunder and the sky was black. ... as the rumbling noise grew louder and the black sky obscured the sunlight, they heard voices singing with drums and bugles sounding and in a few minutes they saw that the black cloud was dust from the horses hooves of a great army of men riding and singing:
- Hurrah, hurrah, we bring the Jubilee
- Hurrah, hurrah, the flag to make you free
- While we go marching through Georgia!
They rode up to the steps, and in less than fifteen minutes soldiers and horses were over-running the place. They came like a crowd of locusts and the noise was so great that suddenly there was bedlam.
280 [The officer] was folding the paper before Vyry realized that the tears were running down her face. Then she turned to back inside her kitchen and her cooking ....
As Margaret Walker explains in her chapter (36) called "A noise like thunder ... / a cloud of dust," General Sherman had burned all the telegraph lines and destroyed train tracks and bridges destroying all regular means of communication, on his march to Savannah and the sea (p 276). As a result, as she explains, the slaves in the backwoods had no news about the progress of or the prevailing victories in the Civil War. It was about four months before the first word of news arrived in the backwoods where Vyry was staying that told about the momentous event that had taken place on January 1, 1864 by order of President Abraham Lincoln.
As Walker tells it, Vyry was cooking in the kitchen when all the children came running in yelling in alarm that a great rumbling thunder was bringing a great black cloud. The thunder turned out to be a regiment of the Union Army singing of the Emancipation and coming to emancipate the now former slaves. When it was over and when Vyry had the document giving her and her children their freedom, with unwitting tears in her eyes, Vyry returned to her kitchen and her cooking, the same as ever but free because the Jubilee had come.
Hurrah, hurrah, we bring the Jubilee
Hurrah, hurrah, the flag to make you free
While we go marching through Georgia!
"Jubilee" is a Biblical allusion to an event held every fifty years in the Judaic religion that liberated all slaves to the status of free citizens and that restored all land that had been sold back to the original family owning it (all land was held by a designated family, by intention, for perpetuity).
Leviticus 25:8-12 (English Standard Version)
“You shall count seven weeks of years, seven times seven years, so that the time of the seven weeks of years shall give you forty-nine years. Then you shall sound the loud trumpet on the tenth day of the seventh month. On the Day of Atonement you shall sound the trumpet throughout all your land. And you shall consecrate the fiftieth year, and proclaim liberty throughout the land to all its inhabitants. It shall be a jubilee for you,...