In 1956 and again in 1963 Dr. King delivered a powerful sermon in the form of a letter from Paul to American Christians, which can be found here. (Please note that his remarks about the Catholic church, which may offend some, were made pre-Vatican II.) There it can be read or listened to. (Note: the script does not correspond word for word to the audio.) A few excerpts from the written text:
[Concerning general morality:]
“You have made tremendous strides in the area of scientific and technological development.
“But America, as I look at you from afar, I wonder whether your moral and spiritual progress has been commensurate with your scientific progress. It seems to me that your moral progress lags behind your scientific progress. … You have allowed the material means by which you live to outdistance the spiritual ends for which you live. You have allowed your mentality to outrun your morality. You have allowed your civilization to outdistance your culture. Through your scientific genius you have made of the world a neighborhood, but through your moral and spiritual genius you have failed to make of it a brotherhood. So America, I would urge you to keep your moral advances abreast with your scientific advances.”
“I am impelled to write you concerning the responsibilities laid upon you to live as Christians in the midst of an unChristian world. That is what I had to do. That is what every Christian has to do. But I understand that there are many Christians in America who give their ultimate allegiance to man-made systems and customs. They are afraid to be different….
“But American Christians, I must say to you as I said to the Roman Christians years ago, “Be not conformed to this world, but be ye transformed by the renewing of your mind.” Or, as I said to the Phillipian Christians, “Ye are a colony of heaven.” This means that although you live in the colony of time, your ultimate allegiance is to the empire of eternity. You have a dual citizenry. You live both in time and eternity; both in heaven and earth. Therefore, your ultimate allegiance is not to the government, not to the state, not to nation, not to any man-made institution. The Christian owes his ultimate allegiance to God, and if any earthly institution conflicts with God’s will it is your Christian duty to take a stand against it. You must never allow the transitory evanescent demands of man-made institutions to take precedence over the eternal demands of the Almighty God.”
“I understand that you have an economic system in America known as Capitalism. Through this economic system you have been able to do wonders…. But Americans, there is the danger that you will misuse your Capitalism. I still contend that money can be the root of all evil. It can cause one to live a life of gross materialism. I am afraid that many among you are more concerned about making a living than making a life. You are prone to judge the success of your profession by the index of your salary and the size of the wheel base on your automobile, rather than the quality of your service to humanity.
“The misuse of Capitalism can also lead to tragic exploitation. This has so often happened in your nation…. God never intended for one group of people to live in superfluous inordinate wealth, while others live in abject deadening poverty. God intends for all of his children to have the basic necessities of life, and he has left in this universe “enough and to spare” for that purpose. So I call upon you to bridge the gulf between abject poverty and superfluous wealth.”
“May I say just a word to those of you who are struggling against this evil. Always be sure that you struggle with Christian methods and Christian weapons. Never succumb to the temptation of becoming bitter. As you press on for justice, be sure to move with dignity and discipline, using only the weapon of love. Let no man pull you so low as to hate him. Always avoid violence. If you succumb to the temptation of using violence in your struggle, unborn generations will be the recipients of a long and desolate night of bitterness, and your chief legacy to the future will be an endless reign of meaningless chaos.
“In your struggle for justice, let your oppressor know that you are not attempting to defeat or humiliate him, or even to pay him back for injustices that he has heaped upon you. Let him know that you are merely seeking justice for him as well as yourself. Let him know that the festering sore of segregation debilitates the white man as well as the Negro. With this attitude you will be able to keep your struggle on high Christian standards.”
[Concerning the goal of life:]
“I still believe that standing up for the truth of God is the greatest thing in the world. This is the end of life. The end of life is not to be happy. The end of life is not to achieve pleasure and avoid pain. The end of life is to do the will of God, come what may….
What is the summon bonum of life? I think I have an answer America. I think I have discovered the highest good. It is love. This principle stands at the center of the cosmos. As John says, “God is love.” He who loves is a participant in the being of God. He who hates does not know God.”"
[Concerning love, the cross, and power:]
“You may have the gift of prophecy and understanding all mysteries. You may be able to break into the storehouse of nature and bring out many insights that men never dreamed were there. You may ascend to the heights of academic achievement, so that you will have all knowledge. You may boast of your great institutions of learning and the boundless extent of your degrees. But all of this amounts to absolutely nothing devoid of love.
But even more Americans, you may give your goods to feed the poor. You may give great gifts to charity. You may tower high in philanthropy. But if you have not love it means nothing…. Without love benevolence becomes egotism, and martyrdom becomes spiritual pride.
“So the greatest of all virtues is love. It is here that we find the true meaning of the Christian faith. This is at bottom the meaning of the cross. The great event on Calvary signifies more than a meaningless drama that took place on the stage of history. It is a telescope through which we look out into the long vista of eternity and see the love of God breaking forth into time. It is an eternal reminder to a power drunk generation that love is most durable power in the world, and that it is at bottom the heartbeat of the moral cosmos. Only through achieving this love can you expect to matriculate into the university of eternal life.”