In these final lines, the grass repeats words and phrases we have heard before: "I am the grass. / Let me work." This grass sure is insistent!
But what does this all mean? What kind of response is this to those train passengers?
Well, first of all, these lines tell us that all the grass wants to do is work—work, work, work. Cover up those battlefields with greenery; let nature do its thing. The grass isn't concerned with history or memory, with consecrating the past or with mourning the dead.
If the grass, or if nature, isn't gonna care, well, then, Sandburg seems to say, it's up to us. And who is this us? Well, how about you and me, for starters?
If we let the grass—if we let nature do its thing, human history will be erased. It's the grass's job to "cover all," but the implication here is that it's our job to remember all.
Sandburg manages to get this message across by creating a sense of distance between the speaker of the poem—the grass—and its human readers. The grass may be personified, but it actually expresses no feelings, concerns, hopes, or joys. It just… works. It just grows—no humanity there.
Because nature doesn't remember human trauma, we have to step in and remember it ourselves. The grass isn't gonna do our job and celebrate war heroes, mourn dead soldiers, or tell our kids and grandkids about the ravages of war. The grass does its job. Through this poem, it seems that Sandburg wants us to do ours.