In Buddhism, we understand that we have committed countless mistakes and have hurt countless sentient beings in the past. In addition to changing our ways, we also have to acknowledge the damage which we have done. Repentance is a process of detailing all the actions we regret and vow to change.
As we repent, we are repenting for ourselves and also on behalf of all other beings who are unable to attend. As a result, we bring all sentient beings closer to awakening through this service.
According to legend, this repentance service was originally composed at the request of Emperor Wu of the Liang dynasty (502–557 CE). Emperor Wu was a devout Buddhist, however his wife Madame Chi, was cruel-hearted and enjoyed harassing monastics until she died.
After her death, the emperor encountered a giant snake in the palace. The snake was tortured by parasites in its scales and was in great suffering. At first, the emperor was terrified, but then the snake spoke to him. The snake said that she was his former wife and begged him to find a way to save her from her miserable state.
Shortly after, the emperor went to ask his monastic teacher, Master Baozhi, for advice. As a result, Master Baozhi led a group of monastics to compose a detailed repentance text that spanned ten scrolls long. The emperor himself participated in reciting the repentance, and upon finishing, he saw a celestial maiden descend upon the palace. She was his former wife who had been freed from her serpent body and now came to thank the emperor for his help.
Since then, this text has been highly regarded in Chinese Buddhism as a way to help sentient beings repent for their karmic transgressions.