The poem sets two options side by side, and the word "or" in the middle makes them feel like a choice the speaker is weighing. One is to live fully in the world, as "present" as a wren, a small bird that moves so quickly it seems to vanish as you look at it. The other is to "unthank all with a gun," a striking phrase that suggests rejecting gratitude, and perhaps life itself, in one violent act.
The last two lines bring the poem indoors and into the body. At night, the speaker hears their own heartbeat and calls it an "enemy of a heart." That makes the heart sound like something hostile, a sound that won't let them rest. The mood is tense, dark and lonely. The wren stands for an ease the speaker wants but can't quite reach, and the poem leaves us in the quiet of the night, unsettled, with the choice still hanging there.