Why is the Preface to Lanting not like a person before and after calligraphy?

In front, the author is lying quietly at his desk. It describes that a group of wise men will meet in Lanting. The scene of drawing water together to make a gift. Cheerful and cheerful. It feels good. So it's written neatly. More natural and free and easy. Next is the author's perception of time and space. I have more emotions. He is bold and unrestrained, writes quickly, even smears, and expresses his feelings incisively and vividly. The same is true of Yan Zhenqing's "Sacrificing a Nephew". This is the value. When you appreciate the Preface to Lanting, what you see is not words, but a kind of spiritual communication. The author is hidden between the lines. You seem to feel his bold talent. He injected great vitality into Chinese characters. So, it can last forever.