The Great Vow to Hear Cries and Save from Suffering
The Mahayana scripture, the "Universal Gate" chapter of the Lotus Sutra, records that whenever beings meet suffering and single-mindedly call the name of the Bodhisattva Guanyin, the bodhisattva "perceives their sounds" and comes to their rescue — hence the name "Guanyin." This promise of compassion "answering every plea" is the core reason for the cult’s wide spread among the people.
The Legend of Princess Miaoshan
The Chinese folk legend of "Princess Miaoshan" tells of Guanyin in a past life as a princess who, defying her father the king to persist in monastic practice, endured many trials and at last attained the Way, cutting off her hands and gouging out her eyes to heal her gravely ill father and moving the whole family with her compassion. This localized story is not found in the original Indian Buddhist scriptures but arose from the blending of Chinese folk faith and Buddhism — an important example of Guanyin’s "feminization and sinicization."