The source and some context for the quote in the final paragraph: [Ref.]

"To Chart Our Course for the Future," by Martin Luther King, Jr.
Address at SCLC Ministers Leadership Training Program, Miami, February 23, 1968,
recording in King Library and Archive, King Center, Atlanta,
in Carson, ed., The Autobiography of Martin Luther King, Jr., p. 351, 342, 343.

I read Das Kapital and The Communist Manifesto, and many of the revolutionary movements in the world came into being as a result of what Marx talked about. The great tragedy is that Christianity failed to see that it had the revolutionary edge. You don't have to go to Karl Marx to learn how to be a revolutionary. I didn't get my inspiration from Karl Marx; I got it from a man named Jesus, a Galilean saint who said he was anointed to heal the broken-hearted. He was anointed to deal with the problems of the poor. And that is where we get our inspiration.

We have the power to change America and give a kind of new vitality to the religion of Jesus Christ. And we can get those young men and women who've lost faith in the church to see that Jesus was a serious man precisely because he was concerned about their problems. The greatest revolutionary that history has ever known.

[Pause]
When I first took my position against the war in Vietnam, almost every newspaper in the country criticized me. It was a low period in my life. I could hardly open a newspaper. It wasn't only white people either.

I remember a newsman coming to me one day saying, "Dr. King, don't you think you're going to have to change your position now because so many people are criticizing you? And people who once had respect for you are going to lose respect for you. And you're going to hurt the budget, I understand, of the Southern Christian Leadership Conference; people have cut off support. And don't you think that you have to move now more in line with the administration's policy?" That was a good question, because he was asking me the question of whether I was going to think about what happens to me or what happens to truth and justice in this situation.

On some positions, Cowardice asks the question, "Is it safe?" Expediency asks the question, "Is it politic?" And Vanity comes along and asks the question, "Is it popular?" But Conscience asks the question, "Is it right?" And there comes a time when one must take a position that is neither safe, nor politic, nor popular, but he must do it because Conscience tells him it is right.