In traditional music, repetition is a device for creating recognizability, reproduction for the sake of the music notes of that specific line and the representing ego.

Why are some sections of music repeated?

“Repetition changes the way we orient to sound,” Margulis said. It tends to draw us into a participatory stance so that we're imagining the next note before it happens.” Music critics and a lot of music fans tend to write off an overly repetitive pop song as trite.

Why do composers use repeating and contrasting sections in their music?

Repetition and contrast also help the listener perceive musical form. The repetition of a phrase reinforces the melody and makes the listener more acquainted with it; then a new, different phrase is introduced (the contrast).