Final answer:
The sentence 'We refuse to believe that there are insufficient funds in the great vaults of opportunity of this nation' most directly refers to the dream that all will be treated equally from paragraph 13 in Martin Luther King, Jr.'s 'I Have a Dream' speech.
Step-by-step explanation:
The sentence We refuse to believe that there are insufficient funds in the great vaults of opportunity of this nation most directly refers to the dream that all will be treated equally from paragraph 13 in Martin Luther King, Jr.'s 'I Have a Dream' speech. In this paragraph, King discusses his dream of racial equality, where people are judged by their character rather than their skin color.