The late Revd Dr Martin Luther King Jr's "I have a dream" speech on 28 August 1963 was one of the greatest of the 20th century. It not only changed the course of race relations in the United States, but also helped to usher in ground-breaking civil-rights legislation. The speech cemented Dr King's reputation as the "conscience of America", and made him a global patron saint for social justice.

When Dr King mounted the podium at the Lincoln Memorial in Washington, DC, that afternoon, he was already regarded as the leader of the US civil-rights movement.

The speech was the high point of the "March on Washington for Jobs and Freedom", when about 250,000 Americans - including clergy of every faith, and a bevy of A-list Hollywood entertainers - marked the 100th anniversary of President Abraham Lincoln's Emancipation Proclamation. Lincoln's declaration had led to the freeing of millions of enslaved African Americans.

Dr King's speech was seminal in substance and style. In front of the crowd in Washington, and millions watching at home, he argued that his dream was part of an American dream that was rooted in the US Declaration of Independence, which proclaimed that "all men are created equal".

In his forceful but polite way, Dr King explained that African Americans were not being unreasonable or idealistic, but asking only for those rights enjoyed by their white counterparts. By embedding these demands within the US Constitution, he was issuing a cogent moral challenge to those Americans who had either ignored or repudiated the case for urgent legislation to guarantee these rights.

EQUALLY, since Dr King came from a long line of preachers, homiletics was second nature to him, and his charisma and eloquence, coupled with a booming baritone voice, made for an orator par excellence. He rose to the occasion that afternoon to deliver a speech that excoriated and inspired.

While the address was short by Dr King's standards, it still allowed him to assume the role of an Old Testament prophet - a modern-day Micah or Amos, who instead of calling for the Hebrews to return to God's covenant standards of righteousness, as found in the Torah, used the US Constitution as the basis of his call for justice.

His speech even quoted Amos 5.4: "But let justice roll down like waters and righteousness like an ever-flowing stream" to reinforce this message. The final portion of the speech is indicative of Isaiah, especially chapters 40-66, which look forward to a world where freedom and fairness reign. King paraphrased Isaiah 40.4-5 when he said: "I have a dream that one day every valley shall be exalted, every hill and mountain shall be made low."

One of the ironies of this speech was that, for someone who often stated that "Jesus's Sermon on the Mount inspired the dignified social action of the civil-rights movement," Dr King made no references to Jesus in his address. Nevertheless, the Lord's call for justice was evident throughout his address, as was Dr King's belief that societal change could take place through moral persuasion and the enactment of legislation.

THE speech proved the zenith for Dr King, who was subsequently seen by many as the person who could steer the US away from racial Armageddon. David Garrow, a noted King scholar, argued that, while he was alive,Dr King saw his task as "redeeming the soul of America". In death, he has become his country's moral compass; someone to whom people turn when looking for support for their campaigns.

This has recently been the situation after the acquittal of George Zimmerman, who was charged with the murder of Trayvon Martin, a 17-year-old African American high-school student. For many African Americans, the circumstances surrounding Trayvon's death in Florida confirm that the civil-rights struggle is not over, and that they need to turn again to Dr King for inspiration.

Some of Trayvon's supporters have been using a doctored photograph of Dr King, draped in a hooded sweatshirt, reminiscent of the one that the student was wearing on the night he died, as a sign of the civil-rights leader's imputed solidarity with the dead youth.

Others, including Stevie Wonder, have called for a boycott of Florida, arguing that Dr King would have supported such a move had he been alive. He was engaged in a difficult campaign to overthrow segregation in St Augustine, Florida, in 1964, and academics recall that he often said that "injustice anywhere is a threat to justice everywhere".

DR KING visited the UK on a number of occasions. On 13 November 1967, after Newcastle University had conferred on him an honorary doctorate, he encouraged all good men and women in this country to "fight against racism in England, the USA and South Africa".

Although Britain has a race-relations record that is the envy of her European neighbours, ours is still a society marked by inequality, in which more young Black British males go to prison than attend leading universities. The unemployment rates and levels of poverty of Black British people are twice the national average, and they have the lowest life-satisfaction ratings of any ethnic group.

As with all such anniversaries, the question how we celebrate Dr King's speech in Britain is vital. Churches Together in Britain and Ireland has produced material focusing on the speech to mark Racial Justice Sunday on 8 September (although it can be used at any time).

Churches could use these resources to celebrate human diversity; to rejoice at how far God's people have travelled together; and to recognise that there is much further to go in both the Church and society.

Christians such as Dr King led the civil-rights movement in the US, and Christians in our country should be at the forefront of campaigns for economic equality and racial justice.

A further way of marking this anniversary would be to support Christian and secular campaigning groups such as the Churches' Racial Justice Network, Church Actionon Poverty, Citizens UK, and the Fellowship of Reconciliation, England, who fight for the type of society for which Dr King lived and died.

Richard R. Reddie is the author of Martin Luther King Jr: History maker (Lion Hudson, 2011).