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.

in ray bradbury's short story "a sound of thunder", mr. eckels's fearfulness leads to drastic consequences for the rest of the world.

in the story, mr. eckels, who is a hunter, hires a time travel company to travel to the age of dinosaurs. although he is excited for the hunting expedition at the beginning, when they reach there and mr. eckels sees the tyrannosaurus, he feels frightened. as he is afraid of the tyrannosaurus, he steps off the path although he has been warned not to do it. by stepping off the path, the entire course of the future is affected: mr. eckart alters the future by stepping on a butterfly, which causes a new man to be elected president in the future. in that way, it is mr. eckart's fearfulness what triggers 'the butterfly effect' and what leads to drastic consequences for the rest of the world.

the time most likely will repeat, in the story.