I think that one way in which prison helped change Piri is that it helped to focus his energies on what was important. Prison causes a maturation in him. It helps him to recognize that individuals can be restored and that change in the individual is possible. He feels a need to "turn his life around" and become more than what he was. Prison causes him to let go of the anger and intensity of emotion that might have driven his poor choices. It is also a moment where he is forced to define himself in terms that transcend racial identity and economic reality.
When he lived in Spanish Harlem, Piri was able to construct his sense of identity in the world through external reality. Anger about racial prejudice and economic challenges consumed him to such an extent that these became the forces that drove him. They were forces that were external in nature, precluding any sort of internal reflection. Prison gave Piri the space to understand his own sense of self away from these conditions. This can be seen even in his idolization of Trina. Prison provides Piri with a realm to define himself as a human being, apart from external reality. In being able to establish a sense of identity apart from the destructive elements of socially constructed notions of what is good, Piri is able to change into an individual who can be redeemed. Restoration is evident in his acquisition of an education. At the end of his prison experience and as a result of it, Piri has earned educational credentials that end up playing a major role in how to define his own sense of self, reflecting how prison has helped to change him.