Amy's poem captures a single chilly Wednesday morning in autumn, and the speaker feels it physically. The cold "pierces" their lungs, the wind "prickles" and "tingles" on bare skin, and the sharpness of the weather seems almost aggressive, as though the season is asserting itself on purpose.
The most striking image is the copper leaves falling like kamikaze pilots into a "green sea" of grass. It turns something gentle into something dramatic and doomed, as if the leaves are sacrificing themselves. The still green "soldiers" in the last stanza continue this military feel, with sunlight teasing them like a playful challenge.
The moon appears briefly, and the speaker questions it directly, wondering why it is out and noting how quickly it comes and goes. That fleeting quality links to the falling leaves: everything here is passing. The mood is crisp, alert and slightly uneasy, mixing the beauty of autumn with a sense of loss and change.