Two short lines hold a small, quiet scene: a bright full moon rises, and a morning glory, a flower that opens with the day, closes up. The poem never says why. It simply lets us watch the flower turn away from the light.
The image works through a small surprise. We usually think of moonlight as gentle and romantic, something to welcome. Here the moon is almost overwhelming, a big, round presence that stares down at the flower, and the flower responds by shutting its "door." That word makes the plant feel like a person retreating into a private home, wanting rest or privacy.
The speaker stays hidden, and the tone is calm and observant rather than emotional. Still, the poem seems to admire the flower's sense of its own limits. The mood is hushed, still, and a little humorous, as if nature has its own good manners.