I first saw this sentence from "Zengguang Xianwen", and later I found out that it comes from "Fayuan Zhulin" in Tang Dynasty: "The six hidden things are like a turtle, and the defense is like a city." , Wisdom fights demons, and if you win, you will be safe." When I was a child, I didn't care when I read this. When I grew up, I suffered a lot for not paying attention to this sentence many times. I felt that this sentence should not be underestimated, and I deeply felt that it contained profound wisdom in life. . Let’s understand it layer by layer.

Defend Yirucheng: meaning: mind, referring to selfish desires. It refers to strictly curbing selfish thoughts and distractions, just like defending a city against enemies.

Buddhism talks about the ten good deeds, which refer to the ten kinds of good deeds performed in the three karma of body, speech and mind, including: not killing, not stealing, not committing sexual misconduct, not speaking harshly, not using double tongue, not No lying, no idle talk, no greed, no anger, no delusion. The key to these ten good karma is mental karma, which is the mind. If the inner defense line is not maintained, it will be even more difficult to protect the other two industries.

The Confucian classic "The Great Learning" talks about "cultivating sincerity and uprightness, cultivating Qi Zhiping", which is based on self-cultivation. It starts from sincerity and righteousness in the body. The achievements of the Qi family in governing the country and bringing peace to the world are all problems that come naturally. Neo-Confucianists summarized it into four words, namely "inner sage and outer king". The heart of a sage is studied internally, and the karma of a king is studied externally. The mind is still the foundation.

"Journey to the West" uses a symbolic method to describe the process of Sun Wukong's apprenticeship and learning in "Lingtai Fangcun Mountain, Xingyue Sanxing Cave" (a riddle of the word "heart"), which is the process of cultivating the heart and mind. The process, and later the Buddhist scriptures from the West, was the process of self-cultivation. The process of Tang Monk's Buddhist scriptures also has this meaning: with the help of Sun Wukong and riding on the white dragon horse, the process of subduing them is to subdue the "horse of mind and mind". He often recited the "Heart Sutra" along the way and experienced ninety-nine and eighty-one difficulties before he became a Buddha. This is also The process of refining one’s mind and becoming a Buddha. According to the book, the demons they encountered along the way were also inspired by greed, anger and ignorance in their hearts. By defeating the demons outside themselves, they also subdued the demons in their hearts. The Buddha said that the difficulty Sun Wukong encountered with the six-eared macaque was also an illusion in his mind. These symbolic meanings all show that if there is a slight difference in intention, there will be a huge loss in achievements, which also shows the importance of guarding one's mind like a city.

Someone has done research on centenarians. They have a unique characteristic, not only good health, but also a good mentality. If the heart is upright, all diseases will not invade. Some people conclude that the mind of defense is like a city, and all diseases will not occur. From this point of view: mind is the most important thing for both body and mind, and guarding against mind is good for both physical and mental health.