The speaker is getting ready for a job that feels both ordinary and enormous. The title, "Essential worker," suggests someone whose labor is needed even when everything seems to be falling apart, and the poem seems to take that idea and push it to an extreme: the workplace is "the world's end." The speaker dresses in "my best instructions," as if the only protection available is a set of rules to follow, not real armor.
The clothing is oddly slight. A "thin nightcoat by day" and a waistcoat at night suggest someone wearing whatever they have, with day and night blurring together into one long shift. The ending is the most striking part: "hot so hot out here / in my hands." The repetition makes the heat feel urgent, and putting it in the hands, the tools of work, makes the burden physical. The mood is tense and weary, but also quietly determined.