Can you cleanse yourself of your sins by literally washing your body? It's debatable. But washing your body can cleanse you of the guilt you feel over those sins. The problem is that might not be a good thing.
The need for ritual cleansing is so common that it has a name: The Lady Macbeth Effect, named after the Shakespearean queen who manipulates her husband into killing the king, and then cracks up entirely and starts trying to wash away the blood on her hands that only she can see. Psychologists conducted a study in which they called people in and asked them to think about their past unethical behavior. They then offered their subjects a chance to receive different items as prizes for their participation. The items were small tokens like pens or pencils, kitchen appliances, and soap products. After only a bit of thinking about their sins, people were far more drawn to cleansers and soaps than other products. The psychological need to cleanse didn't even require water. Subjects were more likely to pick hand wipes as their prize, if that was all that was on offer in the way of cleaning products.
Another study showed that we can get very specific with our Lady Macbeth tendencies. Researchers asked participants in a study to either send a slightly mendacious email or make a slightly over-enthusiastic phone call to the fictitious next participant. When they gave people a choice of prizes they noted that people who had spoken their lies were more likely to go for mouthwash, while those who had written them were more likely to go for hand cleansers.
But should we be absolved of our sin? A symbolic act might make us worse people, practically speaking, in the long run. In one study, people were asked to think of their past misdeeds. Afterwards, half the participants were given a chance to wash their hands, while the other half were not. Those who had washed their hands experienced less guilt and were less likely to agree for volunteer work. In one study, gamblers who had been losing badly and had a chance to wash their hands made riskier bets when they started gambling again. They'd washed away their bad luck, and felt free to court bad luck all over again. Sometimes carrying around your problems is a better choice than letting them go.