There is a pen in your heart, and the pen is talking about calligraphy, which means writing with your heart. Only with the right heart can you write good words. Mu Zong asked Liu Gongquan how to use a pen, and Gong Quan replied: Use a pen in your heart, your heart is always there, and your pen is correct. When Mu Zong was lonely, he changed his face and realized his own remonstrance.
The original meaning is calligraphy, you should write with your heart. As long as your heart is right, writing is a good word. In fact, it is a metaphor, saying that the emperor should be upright and do things that benefit the country and the people. It can also be extended to being a man and doing things, having a correct heart and acting naturally.
Brief introduction of Liu Gongquan
Liu Gongquan is sincere. Jingzhao Garden (now Yaozhou District, Tongchuan City, Shaanxi Province) was born. In the mid-Tang Dynasty, he was an official, calligrapher and poet, and he was the younger brother of Liu Gongzhuo, a senior minister of the Ministry of War. He is a summarizer and innovator of regular script. On the basis of learning and inheriting the regular script styles of Zhong You and Wang Xizhi, he read modern calligraphy, learned from Yan Zhenqing, absorbed his new ideas, and created his own unique "six-style" regular script, which was imitated by later generations and became one of the outstanding representatives of "Tang Shu Shang Fa".
His handwriting is even, thin and hard, and he pursues Wei Bei firmly. His stippling is crisp and beautiful, with thick bones and tight body. "Books are expensive, thin and hard, and the spirit is clear." Compared with his face, his regular script is slightly flat and thin, so it is called "Yan Gu".
Reference to the above content: Baidu Encyclopedia-Liu Gongquan