This article looks at guilt, forgiveness, and "in-group" behavior using Cyprian of Carthage's response to the third-century persecutions in dialogue with modern psychology and the science of guilt. Using Cyprian's writings, we see the foundation of much of Christian behavior in regard to inclusion in a Christian community and the theology of penance. The broader issue of inclusivity and forgiveness connects to what evolutionary science presents on the issue regarding guilt and shame, and recent psychological work on achieving reconciliation and forgiveness between persons or in a community. By placing the Christian tradition into dialogue with these modern scientific studies, we find that a fruitful dialogue is possible which enriches both the religious and scientific communities.