On the surface, this is a set of operating instructions for an office paper shredder: how thick to feed it, what to do when it jams, what to keep away from its teeth. But the instructions keep slipping into something heavier. The "volumes of the past" are "too thick to burn / too dead to resurrect," and the speaker carries "that larger portion of your life" in one arm as they feed it in. The poem suggests someone destroying records of a past they can't keep, though it never says exactly what.
The flat, bossy tone is the point. The speaker seems to hold feeling at a distance by hiding behind procedure, and the shredder becomes a hungry animal that "growls" and has "wide grinned teeth." The line "You wouldn't be here if it weren't necessary" sounds like self-reassurance. The mood is tense, tired and quietly sad, with dark humor in the warnings about hair and scarves. The final rule, "never use reverse," carries the poem's finality: nothing destroyed here comes back.