The title, "Provisions," sets up the poem like a packing list for a journey, but what the speaker gathers is strikingly small: a rose an inch high, and an old, hard-looking moon. Together they seem to be enough.
The speaker sounds settled and quietly sure. "An inch-high rose / shall keep me a while" suggests that even a tiny bit of beauty can sustain a person, at least for now. Then comes a plain statement: no treasure is greater than peace. The poem doesn't argue the point, it simply says it, as if it were obvious.
The last lines turn away from "borrowed mystery," which seems to mean wonder or meaning taken secondhand from other people. Against that, the moon is "this old hard egg," a lovely, odd image that makes it feel solid, familiar, and almost edible, like something you could hold. The mood is calm, modest, and content, with a gentle pride in choosing the simple and real.