The poem is a short, quiet meditation on growing old with someone. It opens with a blunt remark: this isn't weather for the young. That could mean literal harshness, but it also hints that age has its own climate, one that younger people haven't had to face yet.
Then the speaker sets two beliefs side by side. One person trusts the moon, the other the sun. They don't agree, and the poem doesn't ask them to. It seems to be a couple, or two close companions, who see the world differently but share the same fate. The title, "Sublunary," means "beneath the moon," which points to the ordinary earthly world where things change and fade.
The ending is gentle and a little weary. They "turn old," and they rest through both day and night, so neither sun nor moon gets the last word. The mood is calm, tender, and resigned, with a touch of dry humor. Differences matter less than the slow, shared passing of time.