Final answer:
The letter from Thomas Jefferson to Martin Luther King discusses the Missouri Crisis and expresses concerns about slavery's impact on the unity of the country.
Step-by-step explanation:
The purpose of the letter from Thomas Jefferson to Martin Luther King is not specified in the question. However, based on the provided excerpts, it appears that the letter is discussing the Missouri Crisis and expressing Jefferson's concerns about the issue of slavery and its potential impact on the unity of the country. He regrets that the sacrifices made by the founding generation might be in vain due to the ongoing conflict over slavery. Jefferson emphasizes the importance of union and calls for a dispassionate consideration of the consequences of perpetuating slavery.