No difference

"If there is even a bit of difference, it is the remote distance between heaven and earth." This is a famous Zen saying that has been used many times by the masters of the past and present, but what does it mean? Difference between what and what? Allan Marett, roshi explores a famous exchange between Fayan and his pilgrimage companion Hiushan that focuses on this phrase, from the Book of Serenity, Case 17 - 'Fayan's Tiny Bit'.