The mood of Prometheus Unbound undergoes a great deal of change over the course of four acts, beginning rather bleakly with Prometheus chained to his rocky prison, awaiting punishment but determined to be free and strike out against the tyrannical Jupiter. As the play moves from tragedy to triumph, the mood becomes gradually more hopeful, culminating in liberation and forgiveness (of a sort). The indignant frustration and anger fade as Prometheus, grown wise with time, learns to forgive and move on, even as he works towards freedom from oppression. The mood at the end of the play is cautiously hopeful, warning against submitting to said oppression (an apt political message for Shelley's readers) all while maintaining the joyfulness of Prometheus's freedom.
The progression of mood in Prometheus Unbound follows a narrative arc that will be very familiar to anyone who has read the Christian Bible. The Christian narrative begins with Adam and Eve, through whom all of humanity is punished for bringing sin into the world. In the New Testament, Jesus, the Son of God, comes to earth in human form to take all of humanity's sins upon himself and dies to secure forgiveness for humanity's sins. While the mood of the Bible is quite bleak at the beginning, hope is also a definitive element of the story of redemption, much like in Prometheus Unbound. In this dimension, as well as many others, Prometheus Unbound allegorizes the Christ narrative.
