This sentence comes from Su Shi's On Books.
Lun Shu is excerpted from Dongpo Collection, including Su Shi's Lun Shu, Lun Gu Shu and Zi Lun Shu. Su Dongpo's calligraphy is original, not rigid in legalism and not superstitious in authority. He pointed out that "the pen has no definite rules, and it should be empty and wide", and emphasized that the writing style should be free and unrestrained, for one's own use and freedom under the premise of reality.
"Yoga Yu is the best at the beginning of the book" puts forward the highest intangible realm of elephants in calligraphy creation, which is a high-level interpretation of spirituality. His thought of "I can't work hard and never tire of pushing books" has a great influence on later generations.