Four lines are all we have here, and the last one stops mid-thought on the word "Upon". Yet in that small space Shelley sets up a compliment, a pair of images, and a strong sense of the rhythm the rest would have followed.
The subject is admiration. The speaker addresses someone as "thee" (the text never says who) and claims that "Thy beauty hangs around thee like / Splendour around the moon". The central idea is that beauty is an atmosphere rather than a possession. It isn't something this person does or wears. It surrounds them the way a glow surrounds the moon, visible to anyone who looks up. The verb "hangs" matters here. It suggests something weightless and effortless, resting on the air without being fastened to anything. A halo is also not part of the moon's body, so the comparison suggests beauty that is inseparable from the person yet seen at a distance, with a touch of awe. The moon is a remote, cool object, and the simile seems to admire more than it embraces.
The structure is simple and musical. Lines one and three each have eight syllables in a steady, iambic beat ("Thy BEAU-ty HANGS a-ROUND thee LIKE"). Lines two and the expected fourth are shorter, with three beats in line two. This long-short alternation is the pattern of hymns and ballads, a rhythm built to be sung, which suits a poem about a voice. "Like" and "strike" rhyme across the gap, and "moon" in line two seems to promise an answering rhyme in line four. That is an inference from the pattern, but a fair one. "Upon" is not that rhyme, and the line breaks off before a rhyme word can arrive. The quatrain is left with its own sound hanging, as the beauty in line one hangs.
The line breaks do careful work too. The first line ends on "like", so the reader has to pause on the bare word of comparison before learning what is being compared. The simile is stretched across the break, and for a moment we are suspended over the gap. Then "Splendour" arrives, a grand, many-syllabled word, and it wraps around the plain monosyllable "moon". The sentence acts out its own image, with a big shining word circling a small solid one.
The second image moves from sight to sound. "Thy voice, as silver bells that strike" borrows a colour to describe a noise, and the choice of "silver" is shrewd. Silver is also the colour poets habitually give to moonlight, so the two similes quietly connect. The woman's beauty and her voice both end up in the same cool, shining register, as if one image has simply continued into the next. "Strike" is a harder verb than we might expect for something so delicate, but it is accurate, since a bell only rings when it is hit. The voice becomes a single clear, ringing note rather than a soft murmur.
Then comes "Upon". Grammatically it must point at something, perhaps an ear or the air, though the poem gives no clue and guessing is all we can do. A preposition is a pointing word, and this one points at nothing. Whether or not Shelley planned it, the effect is oddly fitting. A poem about beauty that hangs ends with a sentence that hangs, its last word reaching for an object that never arrives.
Shelley is one of the major English Romantic poets, but this scrap is not a famous poem, and its significance is modest. It lies elsewhere than in grand statements. It shows how much a few lines can do: how a simile can be built across a line break, how a metre sets up expectations, how two images from different senses can be bound by a single colour. It also shows the Romantic habit of measuring a person against the natural world, with the moon as the yardstick. And because it is unfinished, the reader can see the scaffolding. We notice the rhyme that hasn't been paid, the sentence that hasn't landed, and we end up, almost without meaning to, trying to finish it ourselves.