why would a rosebud look like a feather bed to the fly?
Answers
This poem is about how normal, everyday objects must look very different to a tiny creature like a fly. The speaker invites us to reconsider the beauty and enormity of both natural and man-made objects, and we're reminded that the size of things is only a matter of perspective. (That is, what's small to us is huge to the fly, and so by extension, what's normally huge to us may actually be small from a different point of view.)
In the first stanza, the speaker introduces his main idea with an exclamation point, saying that everything must look so huge to a little fly ("How large unto the tiny fly/Must little things appear!—"). A flower is the size of furniture to the fly, and a little thorn on a flower is like an enormous weapon ("A rosebud like a feather bed,/Its prickle like a spear;"). These images invite us to consider how a change of perspective can cause beautiful things to be amplified, like the flower that becomes a luxurious bed, as well as frightening things to become even more menacing, like the thorn that becomes a spear.
The second stanza lists three more objects and describes what they must look like to the fly. A drop of dew is like a full-sized mirror to look into ("A dewdrop like a looking-glass,"). A piece of hair is like a shining strand of wire ("A hair like golden wire;"). And a tiny mustard seed seems to have the size and strength of a chunk of burning coal ("The smallest grain of mustard-seed/As fierce as coals of fire;"). These three images take the tiny, relatively insignificant objects around us and bring our view so close to them that they become beautiful and powerful.
Finally, the third stanza lists three more comparisons. Food can look like a huge landscape to a fly ("A loaf of bread, a lofty hill;"). Another insect can be a terrible predator ("A wasp, a cruel leopard;"). Lastly, little grains of salt can seem as dear as baby lambs ("And specks of salt as bright to see/As lambkins to a shepherd."). These final images show us how valuable our food is, how lucky we are to have the advantage of size over a fierce creature like a wasp, and again, how something as common as a grain of salt can be beautiful, bright, and sweet, if we're willing to change our perspective.