Three short lines capture a quiet moment of solitude. The speaker sits up at night, apparently working on letters, and the title "Night shift" gives the hours a feeling of duty, as if writing were a kind of job done while others sleep. Nothing else is happening, so the smallest sounds stand out.
The wind is what the speaker notices. It changes direction, stops, then "beat[s] again," a phrase that makes the wind sound almost like a pulse or a heartbeat. That small detail suggests the speaker is listening closely, perhaps a little restless or lonely, and finding company in the weather. Writing letters implies thinking of absent people, and the wind's pause and return might echo the way thoughts drift away and come back.
The mood is hushed, attentive and a little wistful. The poem leaves a lot of space around its few words, much like the stillness of the night it describes.