Forgiveness
Forgiveness is a main theme of this film. In The Tempest, Prospero must find a way to forgive all those who betrayed him and his family, and in the same way the inmates are seeking forgiveness for the crimes they've committed in order to be set free in their soul and their lives.
Freedom
Shakespeare being worked on behind bars has everything to do with freedom. Of particular interest is the freedom to be shown new, higher ideas about life, rather than living from a low place. Each person has a reason to be free both internally and in the physical world.
Redemption
Redemption is a key theme in this film. Indeed, the men in the film want to be redeemed for the things they've done that have put them behind bars. Their challenge is to prove to themselves and potentially others on the outside that their lives have meaning for good.