Final answer:
The sale of enslaved individuals was a common practice among slaveholders, and Mr. Robert's decision to sell Isabel and Ruth instead of setting them free reflects the priorities and values of the institution of slavery.
Step-by-step explanation:
In the context of slavery in the United States, the sale of enslaved individuals was a common practice among slaveholders. While there may be specific reasons why Mr. Robert sold Isabel and Ruth instead of setting them free, it is important to understand that the institution of slavery dehumanized and commodified enslaved people, treating them as property rather than human beings with rights. Slavery was an economic system that relied on the forced labor of enslaved individuals, and slaveholders prioritized their economic interests over the well-being and freedom of the people they enslaved.