The statement that best explains how the word 'sacred' affects the meaning of the speech is "It conveys King's belief that the goals of the Civil Rights Movement are pure and just in the same way that America's founding ideals are pure and just".
When King talks about 'heritage' in this sentence from "A Letter from Birmingham Jail" he is referring to the founding ideals of the United States, that is, the principles that contributed to build this nation. According to King,<u> these ideals are 'sacred' because they are free from any kind of evil and they always pointed to construct a fair society</u>. Moreover, when he uses the word 'embodied', he is trying to say that the goals that he defends, that is,<u> the goals of the Civil Rights Movement also personify purity since, as well as the founding ideals, these goals also intend to build a fairer society.</u>