A speaker heads home and shuts themselves in. The opening lines treat the walls almost like company: "plaster and brick" are things to "meet with," as if the building were someone waiting. The speaker goes "quiet as the ground," a phrase that suggests both stillness and a kind of burial, a settling down into silence.
The last line explains the whole move. Keeping the doors open might "give longing a home." So the closing is a defense. The speaker isn't shutting out the world out of dislike, but out of fear that wanting something, or someone, would move in and stay. The poem never says what the longing is for, which makes it feel more universal.
The mood is hushed, guarded, and a little sad. The title, "Hermetic," means sealed airtight, and that fits. There's relief in the quiet, but also a hint that the speaker is protecting themselves at a cost.