The speaker is looking out from a train as a heavy rain moves across open country. The scene is simple: clouds racing between green hills, an old barn, horses so small against the land that they look like specks. Yet the poem treats the rain as a kind of relief. The opening suggests it eases the pain of anyone watching from the rusty train, though the poem never says what that pain is.
The mood is calm and quietly hopeful. The horses are said to have "freedom in their veins," and the speaker seems to envy or admire that ease as the wind draws cool waves across the fields. In the last stanza the speaker imagines the whole view as a postcard, getting wet in the rain. That turns the moment into a memory, something to keep. The final image, the rain "looking for a rainbow," ends the poem on a gentle note of expectation.