The ancestral grave of Hong Xiuquan's family is in a place called Zhang Furong in Guangdong. This place is famous for its geomantic omen. It is said that a Mr. Feng Shui named Lai Buyi once visited Guangdong and discovered Long Mai in the north of Guangdong. He thinks that Lotus is the land of Long Mai. He also left a poem saying that he would bury the bodies of his ancestors in Zhang Furong, and the descendants would be princes. This is a folk story. After hearing this story, Hong Xiuquan's ancestors really buried the cemetery in Zhang Furong.
Although Hong Xiuquan was indeed an emperor for more than ten years, it is hard to say whether this is related to Zhang Furong, a land of geomantic omen. However, in the imperial court at that time, the rulers might be worried if they heard that Long Mai was buried in the ancestral grave of Hong Xiuquan's family. Long Mai is only an illusory concept for modern people, but it was a very precious territory in ancient times. The worst thing for a ruler is that someone occupies Long Mai, which is likely to threaten his own rule.
It is not without reason that Emperor Xianfeng was eager to dig Hong Xiuquan's ancestral grave. From the ruler's point of view, no matter whether the legend is true or not, whether the ancestral grave of Hong Xiuquan's family is a treasure trove of geomantic omen or not, it is a big mistake for Hong Xiuquan to covet the throne. Digging his ancestral grave is a small punishment, destroying the geomantic omen of Hong Xiuquan's family, so that he can no longer fight against the Qing government.