The repetitions in "The Love Song of J. Alfred Prufrock" reinforce the idea that Prufrock is trapped in a dull round of activities and petty worries that get him nowhere in life. One example is the repetition of the lines
In the room the women come and go
Talking of Michelangelo.
This implies that the same topics are discussed over and over again by people, causing a numbing effect. This is a party just like a hundred others Prufrock has attended, where people go through the same motions.
The poem repeats the question "Do I dare?" four times, including the following question:
Do I dare
Disturb the universe?
The phrase "do I dare" alliteratively repeats d sounds, putting emphasis on the words that begin with that letter. The fact that Prufrock keeps repeating the question to himself implies that he does not dare to do anything but is caught in a repetitive cycle of timidity that he can't break out of. He finally ends with
Do I dare to eat a peach?
This is a trivial act to worry about: What is daring about eating a peach? This query suggests that he is so caught up in petty concerns that he is not able to see a bigger picture or grab hold of what is important and meaningful in life.
The repetition of the question "And how should I presume?" also indicates that he feels trapped and doesn't know how to break out, especially as it comes after his image of himself as an insect pinned to a wall.
All of this relates to the theme that Prufrock is the representative modern man, too timid and paralyzed to find a way forward in life, unlike the heroes of the past.