After Arsat and his brother run away with Diamelen, they were chased by Rajah's men for Diamelen was a servant of the Rajah's wife. Arsat's brother had a plan to hold the men off while the couple run through the forest. His brother gave them time to run and then plan to catch up with them later. But when the enemies were attacking Arsat's brother, Arsat didn't turn back and helped him. They continue to paddle away leaving him to die. So, the result f the two brothers running away was the death of Arsat's brother because of Arsat's betrayal and cowardice.
This passage shows that Frankenstein is astonished and impressed of his creation ( the monster). It also portrays the fact that he feels proud and happy.
