Into the solemn church, and scatter the congregation, Into the school where the scholar is studying, (3-4)
These lines present us with an image of America <em>before</em> the war: a place of solemn worship and study.
Nor the peaceful farmer any peace, plowing his field or gathering his grain, (6)
Here's a different side of pre-war America: a rural, farming life, where people live in peace, working hard to plow their fields and gather their crops. This peaceful agrarian lifestyle is apparently no longer possible during the Civil War: with a lot of men off fighting, there just weren't enough people to keep things going back on the farm.
Over the traffic of cities—over the rumble of wheels in the streets; (9)
So we've seen the peaceful farmlands, and now we get the hustle and bustle of city life. The traffic and the rumble of wheels suggest that America is a land of industry. But at this point in time, that industry is being overshadowed by the music of war.
No bargainers' bargains by day—no brokers or speculators—would they continue? Would the talkers be talking? would the singer attempt to sing? Would the lawyer rise in the court to state his case before the judge? (11-13)
As we've seen time and time again, the presence of this military band – representative of the war – has changed the complexion of the nation. These lines solidify our impression of America as a place defined by its hard workers: after all, our speaker chooses the disruption of their work as the best way to convey the powerful effects of the war. If these Americans were always looking for an excuse not to work, then it sure wouldn't mean much when they were forced to stop.