The theme of "Raleigh Was Right" is the loss of innocence over time. In the original poem that Christopher Marlowe wrote, "The Passionate Shepherd to His Love," the speaker tries to persuade his beloved to "come live with [him] and be [his] love" in the countryside, where he will give her all sorts of natural gifts. The Walter Raleigh poem "The Nymph's Reply to the Shepherd" features the beloved woman pointing out that the flowers and all the gifts will fade away, as will love itself, and she would be naïve to believe otherwise. The nymph does not have the innocence that the shepherd expected of her.
William Carlos Williams obviously agrees with Raleigh, as his title makes clear. Yet he also goes farther, contrasting his own time with the simpler days in which the original poem is set. His time, he shows, has completely lost the innocence that existed before. Williams wrote his poem in 1944, during some of the darkest days of World War Two. He describes how "the country will bring us no peace" even if they were to go there, because "love itself [is] a flower with roots in a parched ground." Love will not grow in the world, as Williams sees it, whether in the country or otherwise. He points out that both the classical time period in which Marlowe sets his poem and the Renaissance, when Marlowe and Raleigh were writing, were "long ago! / long ago!" He repeats this phrase to emphasize how different things are now given the horrors of his own time period. These earlier time periods may have held some innocence, but his own does not.
Note also that both Marlowe and Raleigh—as well as John Donne, who also wrote a reply to Marlowe's poem during the Renaissance—use iambic pentameter couplets. Williams, by contrast, writes without meter or rhyme, in the free verse mode typical of the twentieth-century. This choice shows that Williams was a man of his time, and it was also typical of his poetry in general. However, the contrast he sets up with the intricately wrought beauty of the poems to which he is responding serves to underline the loss of innocence over time that is the theme of his poem.