Why did Qin become a keeper?

The old dragon in Jinghe near Chang 'an made a bet with the fortune teller and made a mistake. The Jade Emperor sent Wei Zhi to execute the old dragon at 3 noon. The day before, Lao Long asked Tang Taizong to intercede for him, and Tang Taizong readily agreed. The next day, Emperor Taizong announced that Wei Zhi had entered the DPRK and left Wei Zhi to accompany him to play Go. Unexpectedly, at three o'clock at noon, Wei Zhi dozed off and dreamed of beheading the old dragon. Lao Long resented Emperor Taizong's treachery, pestered him, and made trouble in the palace every day, which made the six gods of Emperor Taizong uneasy. Knowing that the emperor was afraid, Wei Zhi sent two generals and Weichi Gong to guard the palace gate. Sure enough, the old dragon dared not make trouble. Emperor Taizong remembered their hard work of guarding the door at night, so he asked the painter to paint their portraits and stick them at the palace gate. The result still worked. As a result, this move began to spread among the people, and Weichi Gong became a keeper.

2. The Romance of Sui and Tang Dynasties contains:

For a time, Li Shimin was in a bad mood. When he sleeps at night, he often hears bricks and tiles thrown outside the bedroom and ghosts screaming, which makes the harem restless every night. He was afraid and told the monarch and his subjects about it. General Qin said: "I have been an officer all my life, killing enemies like melons and collecting corpses like ants." Why are you afraid of ghosts? " I am willing to guard the palace gate with Jingde. "Li Shimin agreed. Nothing happened that night. Since then, I have put two generals on guard every night. Later, Li Shimin suspected that the two men had worked hard, so he ordered the painter to draw the full-length portraits of the two guards hanging at the door, and the evil spirits disappeared from then on. If you are good on earth, you will follow, so the gatekeeper has spread to the people. Up to now, people have always attached importance to the images of Qin Qiong and Jingde.