This study investigates successful completion at a faith-based organization providing residential substance abuse treatment services. Method: The authors apply a complex systems paradigm using a single moderator variable. The participants are primarily African Americans and most have current criminal justice involvement. Probabilities of treatment program completion for participants active in spiritual activities versus similar participants not involved in these activities are calculated. Results: Participation in the spirituality component appears to provide a valuable attractor to treatment completion. Conclusions: In the past decade, evaluation methods have included the greater use of probabilistic approaches, most notably Bayesian inference. Findings suggest that this model, as applied to the complexities of a faith-based organization, is useful for understanding treatment completion. (Contains 3 tables.)