Late at night, someone is still at work, giving instructions in a low, steady voice. The speaker sounds calm and in charge, the kind of person who keeps things running even when the building is quiet. But the second half of the poem undercuts that image. The eyes, which have stopped moving and gone glassy, seem to belong to someone else, and they "might go to bed" without the rest of the speaker's permission.
What makes the poem work is the gap between the voice and the body. The voice carries on being managerial, while the eyes quietly give up. The speaker doesn't complain or announce being exhausted; the tiredness just shows through, almost like a small joke at the speaker's own expense.
The mood is hushed and weary, with a touch of dry humor. Speaking low suits the late hour, and the short lines and plain wording feel a bit like drifting off. It captures that familiar moment when work goes on, but you are barely there.