The poem begins by introducing its central image—the one already previewed by the title:
Rain, midnight rain, nothing but the wild rain [...]
Counting the title, "Rain" is repeated four times in the poem's first nine words! The repetition helps establish the poem's atmosphere and setting. This is a very rainy night, one that makes the speaker feel lonely and somber. As the speaker (whose name, gender, age, etc. are never identified) listens to the rainfall, they think about their own inevitable death:
On this bleak hut, and solitude, and me
Remembering again that I shall die [...]
Because the poem reveals so little about the speaker, it's not entirely clear why their thoughts turn so quickly to death. However, the language in these opening lines suggests several possibilities. The darkness of "midnight" might remind them of the darkness of death; the "wild[ness]" of the rain might remind them of the untamed forces of nature, which eventually overcome all human lives; the "bleak[ness]" of their "hut" might remind them of the bleakness of death; their "solitude" might remind them of the loneliness of the grave. Or all of the above!
Thomas is also known to have written this poem while living in a particular kind of "hut": a soldier's quarters in a military training camp. As an enlisted infantryman in World War I, he knew he would soon see combat in one of the bloodiest wars in human history; indeed, he died on the battlefield the following year. So while the poem never explicitly mentions war, the "bleak hut" detail offers a possible context for its somber tone. (See the Context section of this guide for more.)
These opening lines also establish the poem's form: blank verse, or unrhymed iambic pentameter (i.e., unrhymed five-beat lines that generally alternate unstressed and stressed syllables). This is an old and classic poetic form in English—one associated, for example, with Shakespearean drama. In fact, the poem is a bit like a Shakespearean soliloquy in some ways: it's a solitary meditation on death, love, fate, and other time-honored themes, written in a dramatic and elevated style.
Meanwhile, its sound effects give it a richly lyrical texture: notice, for example, the short /uh/ assonance in "nothing but," the alliteration of "but" and "bleak," the internal rhyme of "but" and "hut," and the short /eh/ assonance in "Remembering again."