What is the primary role of a 'bridge' in a song?

The primary role of a bridge in a song is to provide contrast and lead back to the main theme. A bridge typically offers a departure from the verse and chorus sections, introducing different melodies, harmonies, or lyrical content. This change creates a moment of tension or variation, which heightens the emotional impact and keeps the listener engaged. It serves to refresh the song's dynamic, preventing repetition and monotony, and sets the stage for the return to the familiar elements of the song, often the chorus, that listeners are already emotionally invested in. This structural function effectively enhances the overall narrative and musical development of the piece.