In scripture we find many prophets who come before kings, judges, masses of people, and smaller groups to decree the word of God, call for change, and do it at the risk of their own lives. To read about these prophets you will find that they call out greed, social injustice, idolatry, and rebellion. They were given these prophecies through oral dictation from God, reading God's word, and dreams.
Dr. King had a dream. It wasn't a dream during slumber, but rather a vision of what the world could become. At the time some thought he was a lunatic, some spread rumors against his character, and others followed him wholeheartedly. His dream, however, would flow into the hearts of our country and though still in process begin to change America from white and black to character and content.
Typically when I introduce teaching the prophets, I use some of Dr. King's speeches. He was a prophet, not because he could see the future, but because he proclaimed truth even when it wasn't popular to do so. His prophecy did change our country and brought Christians to a new realization about who the gospel included; everyone.
Dr. King's prophecy has endured through the years. And since we haven't completely realized everything he dreamed it will continue to endure. The dream endures because we are on a journey and because it is true. God spoke through biblical prophets, Martin Luther King Jr. and continues to speak today through others against racism and oppression. We that have ears, let us hear!