Each line of "Origins" names something large that comes out of something unlikely, and each time the result is shrunk down. Milk from stone, ink from sand, liberty from a parliament: the poem keeps using the word "little," as if big things begin in very modest forms. The image of liberty "in a little box" is the oddest and most pointed. It could suggest a ballot box, though the poem never says so. Either way, freedom ends up small and contained, something handed over in a neat package.
The last stanza widens out. From dust come "you and me / and all fooleries," which lumps people in with their own silliness. The speaker sounds wry rather than bitter, a little amused at how humans and their follies come from such plain stuff. The mood is quiet, dry and gently humbling. It doesn't scold anyone. It simply points out that great things, whether nourishment, writing, freedom or us, grow from ordinary, even barren, beginnings.