The poem "Brennan on the Moor" is made up of 13 stanzas. Eleven of these stanzas have four lines (called quatrains) and two of the 13 stanzas have two lines (called couplets)
The content of the quatrains varies significantly from the content of the couplets.
The quatrains tell the story of William Brennan. The first stanza tells how how he was fearless, and the poet says he will tell the story of this "fearless Irishman." We then hear how he began his career.
After the first quatrain, the first couplet appears. This couplet repeats the idea of "young Brennan on the moor" and explains how "brave and undaunted" this young man stood.
The following quatrains continue the story of Brennan. We hear how he was almost like Robin Hood, stealing from the rich to give to the poor. Of course, one day his good fortune had to end, and Brennan was caught by the mayor. Even the mayor's wife weeps when he is caught -- indicating how beloved Brennan was by the community.
The quatrains continue to tell the story of Brennan. He escaped the clutches of the mayor and lived as an outlaw until he was betrayed by a woman he loved. Soon he was taken prisoner and chained in jail until he was condemned to death. The final quatrain are the words Brennan says as he is taken off to his death, as he says goodbye to those who love him.
At the very end of the poem, the second couplet appears. This couplet is exactly the same as the first one that appeared at the beginning of the poem. That is, it reiterates how "brave and undaunted" this young man was.
While the content of the quatrains tells of some not-so-good deeds (robbing and stealing), the content of the couplets emphasizes the goodness (specifically the bravery and fearlessness) of Brennan's character. Furthermore, the couplet functions similar to a refrain of a song. As such, the couplet emphasizes Brennan's goodness despite the many charges that could be laid against the outlaw.
For this reason, the poem ends with the couplet. The poet ends with his goodness -- not his robberies, not his life as an outlaw, and not his death. The poem ends with Brennan young, fearless, and standing on the moor -- forever.
