Sasha Volokh has been writing a series of deeply interesting and thoughtful articles on the phenomenon of the faith-based prison, focusing especially on the effectiveness of faith-based prisons in reducing recidivism and in other ways. Readers interested in the subject will find much to admire in Sasha’s careful and provocative work: see here and here. For criticism of Sasha’s views, see this short reply by Giovanna Shay.
For my own take on faith-based prisons — which focuses neither on empirical nor constitutional questions, but instead on the conceptual position, historical and contemporary, of (religious) penance in punishment theory — see this piece.