Rituals of purification or moral cleansing are common in many religious traditions. For example, ritual washing before prayer, public worship, (re)inclusion, or other religious activities is present in Islam (Wudu), Hinduism (Punyahavachanam), Judaism (Mikvah), Christianity (Baptism), Shinto (Misogi), some forms of Buddhism and Bahai. For believers, ritual washing is a physical act with moral effects: the water washes away moral impurities more so than material ones. It is often said that forgiveness is good for the soul, but is it really good for one’s character? There’s some evidence to suggest that it may not be.
In a series of often-cited studies, researchers Chen-Bo Zhong, and Katie Liljenquist found that a guilty conscience heightened one’s desire for physical cleansing. However, once the cleansing was complete, the individual was actually less interested in helping others. In their study, Zhong and Liljenquist asked people to recall in detail an ethical or unethical deed committed in their past. Later, those who recalled an unethical deed were significantly more likely to select antiseptic wipes over pencils as a post-experiment gift. Ironically though, those who selected the antiseptic wipes 
and used them to clean themselves were less likely to volunteer to aid another student compared to those who did not use the wipes.
Thus, awareness of moral transgression prompted individuals to seek physical cleansing; but once (symbolically) cleansed, individuals were actually less motivated to behave altruistically. This suggests that rituals of absolution may make people feel better, but they don’t make people behave better. Unburdened by a guilty conscience, the newly absolved lapse comfortably into moral complacency.
But maybe it’s premature to toss out the holy water. A more recent study suggests that confession may indeed prompt altruism. In this study, Catholic subjects were asked to recall both committing a sin and receiving absolution for the sin by going to confession. The subjects were also given an opportunity to make a donation to a local Catholic church. For half of the subjects, giving the donation came after they recalled receiving absolution, while for the other half it came before recalling receiving absolution. Those who donated after absolution contributed significantly more than those who donated before absolution. Thus, in contrast to the previous study, recalling the experience of absolution (of having one’s sins ritually washed away) actually led to greater prosocial behavior not less.
The authors offered a number of possible explanations for the result. First, they noted that this was within-group altruism while previous studies may have required participants to behave altruistically to perceived out-group members. (They do note, however, that there are real-world instances of what appears to be ritually-mediated out-group altruism). Second, they found that positive emotions were often associated with confession and absolution. These positive emotions may have motivated greater generosity. Third, the confession ritual may have “primed” or subtly brought to mind religious notions of normative behavior and supernatural judgment which served to stimulate generosity. Finally, the authors raised the possibility that verbal confession (unlike physical washing) may encourage one to re-live sinful acts, which increases feelings of guilt or moral responsibility and this encouraged restitutional acts.
Undoubtedly, more studies are needed to sort out the relationship between ritual cleansing and altruistic behavior. One thing seems clear, however. Absolution may be good for the one absolved, but it is not necessarily beneficial to the community. For that, it may have to be coupled with an additional step – penance.
Refs:
Chen-Bo Zhong, Katie Liljenquist 2006 Washing Away Your Sins: Threatened Morality and Physical Cleansing, Science, 313, 1451-1452.
Ryan McKay, Jenna Herold & Harvey Whitehouse (2013) Catholic guilt?Recall of confession promotes prosocial behavior, Religion, Brain & Behavior, 3:3, 201-209