Li begins the film by abandoning the spiritual (monastic) life, reentering the world of swordsmanship, and letting himself be led by his deep passion for Yu. Even as he dies, he says he'd rather be a ghost by Yu's side than enter nirvana.
Jen begins the film totally enveloped by narcissism and passion. By the end, she abandons these attitudes and her boyfriend for an act of spiritual redemption (jumping off the mountain).
So Li and Jen trade places. Having two major characters trade places can give depth to a plot.