Nathaniel Hawthorne was an American novelist and short story writer who lived in the mid 19th century. He has adopted the style of "Dark Romanticism", which is focused on reflecting people's interest with the irrational or grotesque. His work was characteristic of using many metaphors.
In this case, he focused on getting the reader to get full details on the march of people as a build-up for a main event in the story, which, was soon to come afterward. The reader learns what are the people thinking or going through as they march.