Most poems about night either fear it or sink into it. Shelley's speaker does something more unusual: he waits for Night the way a lover waits for someone who is late. Across five stanzas he calls her forward, confesses how dull the day has been without her, turns down Death and Sleep when they offer themselves, and ends with the same plea he began with, "Come soon, soon!" The central idea is that what he wants from darkness is neither rest nor extinction. He wants Night herself, the dreaming, imaginative state she brings.
The imagery makes her a creature of texture and touch. In her "misty eastern cave" she "wovest dreams of joy and fear," so she is a weaver, and dreams are things made by hand. She wears a "mantle gray, / Star-inwrought," a cloak stitched with stars. Her hair "blind[s] the eyes of Day," and she kisses Day "until she be wearied out." Then she travels over "city, and sea, and land" with an "opiate wand," a phrase that mixes magic and medicine, as if darkness were a gentle drug. Day is the opposite. Noon "lay heavy on flower and tree," and the afternoon lingers "like an unloved guest." The poem reverses the usual idea that daylight is cheerful and night is threatening. Here light is a bore who won't leave. One small oddity is that Day is "she" in the second stanza and "his" in the third. The poem seems more interested in the feeling of each figure than in keeping a tidy allegory.
The fourth and fifth stanzas hold the poem's real argument. Death and Sleep appear as Night's brother and child, a family gathered around her. Sleep is "filmy-eyed" and murmurs "like a noontide bee," a soft, drowsy picture that makes the speaker's blunt answer, "No, not thee!", all the sharper. The final stanza explains the refusal, though it asks the reader to work. "Death will come when thou art dead" and "Sleep will come when thou art fled" suggest that both depend on Night's absence or end. Judging by the logic of the lines, they are what remains once her dreams have gone, blank where she is vivid. Death will arrive "soon, too soon" without being asked, so he needs no invitation. The "boon" the speaker wants is something only Night can give.
The form carries this urgency. Each stanza has seven lines of uneven length, and the rhymes echo across the stanza without settling into a rigid pattern: "wave" with "cave," "Night" with "daylight" and "flight," "thee" with "tree." Each stanza ends on a short, pleading line: "Swift be thy flight!", "Come, long-sought!", "I sighed for thee," "No, not thee!", "Come soon, soon!" These work almost like a refrain, and they pull the poem back to its single desire each time. The lines are short and mostly built on three or four stresses, and the opening "Swiftly walk" begins on a hurried beat. Key words keep repeating: "swift" in the first stanza, "sighed" twice in the third, "soon" three times in the last. The reader hears the speaker's impatience in the sound.
The poem matters because it takes a familiar Romantic gesture, speaking directly to a personified force of nature, and makes it intimate and a little daring. Night is "terrible and dear" at once, and the poem never pretends she is simply comforting. Choosing her over Death and Sleep also gives it an idea to argue about: the speaker prizes heightened, dreaming consciousness above both rest and ending. Whether you read that as hope, escapism, or a longing for imagination, the poem makes you feel how badly he wants it.