Why might songs be used in the presentation of key themes in ‘Blood Brothers’?

The use of songs in Blood Brothers is rather like a Brechtian technique - it breaks the fourth wall for the audience and so, we listen more closely to the lyrics. They also help to contribute to the mood of the play - many of the repetitions to Marilyn Monroe give us a feel for the past, and the desire to live a different kind of life which is what many of the characters in the play aspire to.