The Heart Sutra is a short philosophical work central to many schools of Mahayana Buddhism, including Zen Buddhism. The doctrine of the heart sutra, such as it were, is that not only is illusion an illusion, but the realization of the illusion is equally an illusion. It strikes down both grasping and rejection.
That of course, is the very short version. I would suggest that everyone go and read a good translation. However, apart from the Heart Sutra itself, the effect of the work on various other works of Chinese literature is immense. The Heart Sutra is one of the treasured works sought after in the Journey to the West, and the use of it transforms The Red Chamber Dream from a soap opera to a story of transcedental human nature.
The Heart Sutra is in many ways used because it is the crowning statement of the common metaphysics that Buddhism, Taoism and Confucianism, that told of the differentiation of Heaven into Earth, although of course it got more complicated then that. Thus, knowing that Emptiness was actually Form, and vice-versa, the boxing match between a monkey and some brigands actually represents some universal principle, and a quarrel between two teenagers is actually a cosmological discussion.
Being the Otaku that I am, I wonder how far the influence of the Heart Sutra has spread. I find reflections of its belief in all sorts of gnostic space operas that I have read. I think of it when I think of Cloud and Tifa at the Northern Crater, with Cloud telling Tifa(reth?) that he wants to meet Aerith in "the Promised Land". I think of it in the phrase "the Fish jumped out of the water". Truly, it foretells "all legends and prophecies fulfilled".
The Heart Sutra provides the perfect framing metanarrative for any story, because it can keep track of anything by measuring it's distance from nothingness. But the very fact that it can do such a thing is only because it is so strongly anti-narrative in doctrine.
all things are essentially empty--not born, not destroyed
not stained, not pure, without loss, without gain,
It would seem with no ideas of beginning or ending, of losing or gaining, that narrative would be impossible. Narrative is about change, and if there is no change, there can be no narrative. The Heart Sutra is not about a battle of good vs. evil, even in such a subtle way as a battle of wisdom vs. ignorance. It is not about characters moving towards perfection, even in the form of kong
Why it would be adopted as a benchmark of cosmological progress then, is an open question. The higher answer is that only by being an empty metanarrative can it allow smaller narratives to exist at all, and thus validate them. The lower answer is that most Chinese people enjoyed watching operas with monkeys handing people a beat down more than trying to gain insight into the nature of the universe.
But the story of Lin Dai-yu still seems even more tragic for me because of "what it meant".