Five short lines, and the whole poem is an act of listening. Almost nothing happens in it. The air is "clear and very cold," a squirrel is working at a nut, and a bird starts to sing. The central idea is that this is enough. Paying close attention to a small moment and finding the exact comparison for it is a way of being fully awake in the world.
The poem has no rhyme and no regular meter, so it belongs to free verse, and its shape does a lot of the work. The first three lines are short and clipped. "Clear and very cold" is not even a full sentence, just plain words laid down like a thermometer reading. Then comes the poem's only "I," in "I hear," and the speaker vanishes again. We learn nothing about his thoughts or mood, only what reaches his ears. The title, "Morning Porch, the book?", places him somewhere that is neither indoors nor quite outdoors, which seems a good spot for listening. The question mark is odd, and the poem itself doesn't explain it, so I would not guess at what it refers to. The last two lines stretch out, and the lengthening feels like the morning loosening up.
The sound of the words matters as much as their meaning. "Squirrel teeth / on walnut shell" is a startling image, since we hear the teeth rather than see the animal. The line break leaves "squirrel teeth" hanging for a moment, and then "walnut shell" lands with two heavy syllables side by side, slow and crunchy. The consonants are hard and brittle: t, th, k, the closing l. In the cold stillness, one suspects, such a tiny noise carries a long way. The poem implies this rather than saying it, and perhaps that is also what "clear" means, for sound as well as sky.
The poem's best invention is the "happiness motor." The bird is named with precision, a Carolina wren and not just "a bird," and then it is renamed with a coined compound that joins an emotion to a machine. The next line develops the metaphor as if the bird were a stubborn engine: it "turns over once, twice, then putts to life." The counting makes us wait, and the commas act like failed attempts to start. The verb "putts" is onomatopoeia for a small, modest engine, nothing like a roar, and it is faintly comic in a way that suits a small, loud bird. The metaphor also grows out of the first line. Cold engines are reluctant to start, so the "very cold" of line one quietly explains the sputtering of line five. The wren seems to warm up the day the way a driver warms up a car.
"Putts to life" works on more than one level. It describes an engine catching, but it also describes a creature, and a morning, coming alive. The squirrel's gnawing and the wren's song are both small, busy sounds, and the poem sets them side by side. One seems to belong to appetite and the other to joy, though the poem does not spell that out. "Happiness" is the only abstract word in the whole text, and it is given to a bird, not to the speaker. Judging by how carefully the scene is heard, though, the speaker shares in it.
The poem is significant because it manages so much with so little. Its brevity and its attention to weather and creatures echo the haiku tradition, but it chooses its own rhythm and uses a modern, mechanical image where we might expect something pastoral. It also ends without commentary, with the engine running and the song just beginning. A reader is left with a cold porch, a warming sound, and a reminder that the ordinary world becomes vivid when we listen closely enough to compare a wren to a motor and find that the comparison is exactly right.