As an imported religion, the missionaries had made a great efforts on integrating Buddhism with Chinese inherent culture when they were devoted to propagate it into China at the very beginning. Without violating Buddhist teachings, all endeavors were to enable Buddhism to have a smooth development and widespread over the country. Su-jiang (i.e. secular preaching) was one of the methods, adopted and prevailed in the Tang dynasty, for immersing this originally foreign religion itself in the local culture.
Su-jiang, dating back to the Six Dynasties, is a way aimed at expounding Buddhist sutras for secular people; in so doing, it helps them to comprehend the abstruse texts of Buddhism and ultimately comes to make well known about Buddhist doctrine (dharma) and preach widely the teachings. This propagating way was actually in vogue during the eras from the Tang to Five Dynasties. Moreover, the so-called Bianwen can be seen as texts of Su-jiang, in which it is a literary form invented for the convenience of doing missionary work. Bianwen is believed to be derived from the partial content of sutras (Buddhist scriptures); after derivation, adding and editing by the creative styles of narrators and chanters, it has transformed into stories that the public can easily understand.
At the ancient time, Confucianism (a.k.a. Ruism, originated from the Spring and Autumn Period) was not only a system of ethical-sociopolitical teachings, but also the mainstream thought; in addition, filial piety has always been one of the most important virtue in Confucian philosophy. Therefore, Mulian Bianwen is a narrative which takes "respect for parents" and "repay the grace and loving-kindness of parents" as the core of storyline, which nicely blends into the distinctive way of carrying out piety in Buddhism. The actions and events, such as being a monk (or nun) to practice Buddhist rules and holding Yulanpen Hui (i.e. Ghost Festival), have made a greater promotion for Confucian piety. Undeniably, that's had brought Buddhist filial thought being successfully popularized and accepted by the folks for a long time.
After comparing the differences in thoughts between Confucianism and Buddhism, we could find that Mulian Bianwen first syncretized Confucian philosophy, and then used dramatic story plots to preach the viewpoints of the Buddhist filial thought to the crowds. This development made “Mulian Rescues His Mother” the most popular Buddhism tale during the Tang and the Five Dynasties. Afterward, though Bianwen had been banned at the time of Emperor Zhenzong of Song, the tale of “Mulian Rescues His Mother” never died out and spread down by the forms of Baojuan (texts written in an alternation of prose and verse) and dramas. Eventually, Mulian has been becoming the most representative figure of the Buddhist filial thought.