Rain falls through the whole poem, and with each repetition of "It's raining" the scene widens. We start with gutters clogged by ice, then move to buds, worms, and finally an ant queen under a log. The speaker seems to be a quiet observer on a rural property, watching rather than commenting, and the feeling is one of gentle wonder.
The big idea is thaw. Winter's grip loosens, and everything small begins to stir. The images are playful and a little grand: downspouts "gargle," the frost leaves "palaces" in ruins, and bulbs will "write their deathless names in the air." Even the pregnant barn cat suggests new life on the way. The ending is the quietest moment. The ant queen simply "resumes her slow march," as if spring is less a burst of energy than a patient restart. The mood is calm, fresh, and quietly hopeful.