The poem seems to follow a discarded sack, probably a plastic bag, as it blows around a city. The title gives the clue: like a tumbleweed, it drifts "up and down / to many places" with no destination of its own. The images are small and quiet, and the poem never says outright what the object is.
The most surprising moment comes when the sack "begins / to want its color." Something empty and thrown away is given a longing, as if it could remember what it once was or wish to be vivid again. Then the poem shifts to something almost magical: the bag is "like a spirit of water / returned to the yard," which suggests it may be filled out by wind or rain and seems to carry a living presence.
In the last two lines, the speaker's feeling comes forward. The heart finds "a true grammar" in this ordinary scrap, a kind of meaning or order. The mood is tender and curious, a gentle surprise at finding something moving in litter.