"The Mountain" (Paragraph 12) symbolizes a problematic struggle or consequence.
"The Mountaintop" (Paragraph 12) symbolizes the end or conquering of a problem that someone had to face.
"The Promised Land" (Paragraph 12) references heaven, but it symbolizes a world where no one will be judged or labeled by their race or skin tone/color.
"Mine eyes have seen the glory of the coming of the Lord," (Paragraph 12). This does not mean that he has seen God on Earth, but rather he has seen what the change of world equality is going to be like.
"Take a ride for freedom," (Paragraph 4). This is a metaphor, since you cannot actually ride for freedom, as it is not an actual item.
"A man cannot ride your back unless it is bent," (Paragraph 5). This is an idiom. It actually means that you cannot help someone else without carrying a burden among yourself.