How to understand the moon and the green willow?

The Monk Crossing the Green Willow in the Moonlight is selected from Yu Shi Ming Yan and Yuan Zaju.

Generally speaking:

Yang Liuzhi in the clean bottle of Guanyin Bodhisattva in Nanhai was sent to the world as a prostitute, named Liu Cui, because she was occasionally contaminated. Thirty years later, the venerable Luohan Yueming became a monk. After three statements, Liu Cui woke up and ascended to heaven.