The speaker begins modestly. The only help on offer is "the sound of an evening," something small and fleeting rather than a grand comfort. Alongside it comes "a large desire" for "my old friend, the world," which sounds warm and a little wistful, as if the speaker feels close to the world but not quite held by it.
Then the last two lines turn sharply: "Nature is the first lie / since coming from sea." The idea seems to be that "Nature" is a story we tell ourselves, an idea laid over the real, messy world. The mention of the sea suggests an ancient origin, a long distance travelled from where life began. The title, "Against Nature," backs up this sense of resistance.
The mood is thoughtful, tender and slightly skeptical. The speaker loves the world but doubts the word "nature," and the poem leaves that tension open rather than settling it.