Answer:
It makes the threat more serious because, although slavery has ended, George has more rights than Mitchell does.
Explanation:
In Mildred D. Taylor's novel "The Land", the plot of the story revolves around the life of Paul-Edward, a biracial child whose father is a former slave owner and mother was a black slave during the plantation days. But even though Paul is mixed, his father did all he can to make sure that he is brought up along the same circumstances as his white brothers.
The given excerpt from the text shows the character of George in conflict with Mitchell, the son of one of their workers. Though the actual system of slavery has ended, there still seems to be a power dynamics in play. George, being the son of the master, acts all high and mighty with Mitchell, who is just a mere son of one of their workers. The threat to decapitate Mitchell's head seems a serious one for George still has more rights than Mitchell.