Why have two different types of stanzas been used to structure ''brennan on the moor"?

The two different stanzas are the alternating stanzas of four lines and two lines, all with a consistent rhyme scheme. In the poem "Brennan on the Moor", each four-line stanza describes a new episode that continues the story, while the two-line stanzas repeat the same phrase about the main character, like a chorus.

she feels sorrowful and regretful. helen felt delight after breaking the doll.  

hope this

the answer should be:

the intervention of the supernatural gives gilgamesh hope that he will defeat humbaba.