To scatter plenty o'er a smiling land,And read their hist'ry in a nation's eyes,Their lot forbade: (63-65)
The speaker points out that the villagers' situation (their "lot") kept them from making a big splash in the history books. After all, they were pretty busy just keeping food on the table!
Along the cool sequester'd vale of life They kept the noiseless tenor of their way. (75-76)
The villagers had to live their lives in the seclusion of the village—outside of the national spotlight. They didn't make a lot of "noise," in that they didn't do anything that got recorded in the history books, but that doesn't mean that we should just forget about them.