How has the meaning and significance of Briony's play The Trials of Arabella changed since she wrote it? How does its length matter, when actually performed?

The significance of the parallels between the novel Atonement and the play within the novel, The Trials of Arabella, become clear by the end of the novel. Though the happy ending in the play is impossible, considering the realities of war and life that Briony has experienced in her long life, she still has a childish dream of a happy ending. The meaning of this immature desire intensifies in its poignancy by the end of the novel as the reader knows exactly how Briony herself ruined any chance of a happy ending for people close to her.
The length of the play matters because the play represents the novel in which it is contained. Atonement, a full-length novel, is much longer than the play, a mere five pages, but the framework of both pieces of writing are similar. The conflicts and trials that impact the characters in the play are similar to those that impact the characters in Atonement, but their story is condensed into a much briefer experience for the audience.