In a world in which most "literature" was memorized and then performed orally, repetition had a few key functions: 1) making it easier to tell a part of the story (an audience probably wouldn't listen to the whole thing in one go); 2) making it easier to memorize (while also allowing the performer/bard some time to "autopilot" and remember what comes next); 3) making the meter fit (this is why you'll see the same epithets over and over).