Here:
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. You have become the richest nation in the world, and you have built up the greatest system of production that history has ever known. All of this is marvelous. 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. They tell me that one tenth of one percent of the population controls more than forty percent of the wealth. Oh America, how often have you taken necessities from the masses to give luxuries to the classes. If you are to be a truly Christian nation you must solve this problem. You cannot solve the problem by turning to communism, for communism is based on an ethical relativism and a metaphysical materialism that no Christian can accept. You can work within the framework of democracy to bring about a better distribution of wealth. You can use your powerful economic resources to wipe poverty from the face of the earth. 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.
I would that I could be with you in person, so that I could say to you face to face what I am forced to say to you in writing. Oh, how I long to share your fellowship.
http://www.stanford.edu/group/King/publications/sermonsFrame.htm