These characters combine to create a vivid metaphor: to “wash the heart” is to purify one's inner self, and to “change the face” is to alter one's external actions. Together, they describe a complete, inside-and-out reformation.
`洗心革面` is deeply rooted in Chinese philosophical traditions, particularly Confucianism and Buddhism, which emphasize self-cultivation, moral rectification, and the potential for redemption. The idea that a person, no matter how flawed, can achieve a state of inner purity (`洗心`) through sincere effort is a cornerstone of these beliefs. To an English speaker, “to turn over a new leaf” is the closest equivalent. However, `洗心革面` carries a much greater weight. “Turning over a new leaf” can sometimes be used for relatively minor changes, like starting a new diet or quitting a small bad habit. In contrast, `洗心革面` is almost exclusively used for major, life-altering moral transformations. It implies a conscious and often difficult struggle to overcome a seriously flawed past (e.g., crime, addiction, corruption) and is seen as a highly virtuous and respectable act. It speaks to the cultural value placed on sincerity, repentance, and the profound journey of becoming a better person.
This idiom is formal and literary. You won't hear it used in casual, everyday slang, but it's common in more serious contexts.