In Walt Whitman's poems, "A Sight in Camp in the Daybreak Gray and Dim," and "I Hear America Singing" are very different poems.

The tone of "I Hear America Singing" is a positive one. Whitman identifies a variety of people at work, who sing as they complete their respective jobs: mechanics, carpenters, masons, the shoemaker, among others, as well the the mother, or girls washing or sewing. All of these people sing as they work, content (it would seem) with the tasks before them.

The delicious singing of the mother, or of the young wife at work, 
or of the girl sewing or washing, 
Each singing what belongs to him or her and to none else, 
The day what belongs to the day

The repetition of the word "sing" provides a sense that Whitman is focusing on the songs these people sing: different songs, but still uplifting and satisfying to the singer and the audience.

The movement of one person singing and then the next, and the next gives a sense of the movement of song, the cycle of days within a society, of the daily tasks life demands that we complete with song. And music is an international language. I don't think the poem is as much about loving America as the unity of its people as they live a life there, satisfied in their work—and all singing.

However, the tone is much different. This poem, about the Civil War, speaks of a man leaving his tent early one morning, unable to sleep, when he sees "three forms lying on stretchers."

...untended...lying,
Over each the blanket spread, ample brownish woollen blanket,
Grey and heavy blanket, folding, covering all.

There is clear meaning if one reads the details carefully:

Each form is untended: the implication is that each is beyond help. Brown woolen [heavy, suffocating] blankets cover each figure, cover ing all—the faces are also covered, which signifies death.

The man, curious to know who has passed sees the face of an old man; the next is the face of a young man, "cheeks yet blooming." The first man we understand has passed and with years behind him, we can more easily handle his loss. The second takes us aback: a young boy has died before beginning to live.

The third is the one that stops the reader in his—or her—tracks.

Then to the third--a face nor child, nor old, very calm, as of
beautiful yellow-white ivory;
Young man, I think I know you--I think this face of yours is the face
of the Christ himself;
Dead and divine, and brother of all, and here again he lies.

This line draws our attention to the brotherhood of all men, all in the image of a benevolent Christ: Whitman wants the reader to see that each loss is tragic: regardless of age. In death, all are divine, all are bothers, and the sense of loss for each is the same as if Christ were there among the other two: as if Whitman points out mankind's connection to God—connected here in death.