The relationship of the bold and underlined sentence is that they are both on the related subject of racism. In the underlined sentence, it is describing the absolute nonsense for a community to be racial in such way as to burn and bomb Negro homes and religious places (bold sentence). So, once again, the main purpose of both sentences is that they are describing that racial prejudice shall not be allowed and shall not take over one's community.
I do hope I helped! If I was not somewhat correct, I apologize dearly. Thank you.