Martin luther king jr (state a specific figurative language device) and (state a different specific figurative language device) to convince (who is the letter written to? tip: see first line of letter! ) that (insert king's message or purpose for writing the letter). 

Answer

Martin Luther King Jr uses personification (state a specific figurative language device) and metaphors (state a different specific figurative language device) to convince critics (WHO is the letter written to? TIP: See FIRST line of letter!) to inform those who were initial ignorant to the true nature of their causes, letting people know their struggles (insert King's MESSAGE or purpose for writing the letter).

Explanation

Martin Luther King Jr, wrote the letter to respond to the criticism that were connected to his work while he was in jail in Birmingham. The letter aimed to respond to spreading criticism with regard to the Civil Right Movement and MLK. The primary audience were those that spread the critics and in broader explanation, it was meant to reach all those individuals who did not understood their cause including those that were arrogant about what they were fighting for in the first place. Metaphor was used to compare injustice to a boil. Personification  was applied in the letter where  MLK self-compare to Apostle Paul from the Bible.

umm there is no difference

great question btw!