Martin Luther King speaking at Vermont Ave Baptist Church in Washington in 1968. (Matthew Lewis/The Washington Post)
Patrick Lacroix teaches U.S. history at Bishop’s University (Sherbrooke, Quebec).

Today, we pause to remember the life and work of Martin Luther King Jr.

But which King will we remember? Undoubtedly, most Americans will reflect on King’s role in civil rights. As some historians remind us, we should also remember his participation in the antiwar movement and his campaign against economic injustice.

There is yet another Martin Luther King that we often forget — one who takes us back to the religious ferment of the 1960s.

As a young Baptist pastor, King was steeped in black prophetic religion. To the cause of racial justice he brought a rhetoric and religious vision that captured African Americans’ centuries-long struggle for equality, a faith that was always in conversation with the evils of the world.

This vision did not merely promise spiritual goods. As a kind of liberation theology (one that emerged before the Roman Catholic liberation theology), it suggested that peace, freedom and equality were achievable here on earth, if we only lived up to the moral teachings and injunctions of the Gospels.

Most Americans think of the 1960s as a secular decade that witnessed the apogee of activist government. But it was actually the heyday of the religious left, a movement that animated and propelled that activist government forward. The liberal interfaith coalitions of which King was the foremost actor marked a new and important chapter in American politics and American religion. Overshadowed by the conservative reaction that appeared in its wake, its successes have since been forgotten, despite their revolutionary consequences.

In the early 1960s, prophetic religion began interacting with the liberalism of Northern Protestant seminaries and the modernizing impulse given to Catholicism by Pope John XXIII. Predominantly white denominations imbibed the language and aspirations of this prophetic religion, not content to bless an idealized American way of life, but rather seeking a more just society. Tentatively, as Catholic-Protestant tensions declined during the Kennedy years, arms were linked across denominational borders in the interest of social justice.

These forces broke through in the summer of 1962. In Albany, Ga., white clergy — Catholics, Protestants and Jews — joined King in significant numbers in civil rights protests and acts of civil disobedience. The newfound fervor among these clergymen was such that many relished the jail time that awaited them. In fact, their incarceration helped to awaken consciences across the country as ordinary worshipers grappled with discriminatory applications of “law and order” in the South.

Few events better exemplified the new religious realities than the Conference on Religion and Race held in Chicago in January 1963. More than 600 delegates attended this interracial and interfaith event, organized to explore how Christians and Jews might advance civil rights. They declared racial justice an urgent moral issue, demanded legislative action and committed the means of their churches and synagogues to the cause.

On the final day, King declared, “In this area the Church has failed Christ miserably. In the midst of a nation rife with racial animosity, it too often has been content to mouth pious irrelevances and sanctimonious trivialities . . . it has too often remained silent behind the anesthetizing security of stained-glass windows.”

King was adamant: “If the Church does not recapture its prophetic zeal, it will become little more than an irrelevant social club with a thin veneer of religiosity.” These words echoed a Baptist pastor from Virginia who a year earlier had exclaimed, “May God help us if we remain in our ivory towers of institutional churchism, in our self-righteous, status quo White supremacy Southernism, or in a state of isolationism from the suffering majorities of this world.” Faith could not be severed from the most pressing questions of the day. It entailed a duty to the world; it demanded action.

It is this simple proposition that underlay King’s famous “Letter from Birmingham Jail,” penned in April 1963, as indeed it did the religious left as a whole.

In encounters with American politics, the activists found their faith fulfilled. In June 1963, President Kennedy echoed their rhetoric in his national televised address on civil rights, an issue that he framed as a matter of moral justice. Later that month, Kennedy welcomed hundreds of clergymen to Washington to discuss the place of religious institutions in the struggle for racial justice.

When hundreds of thousands of Americans converged on the March on Washington in August 1963, an unequivocally religious affair awaited them. The Catholic archbishop of Washington delivered the invocation. Accompanying him on stage was Father John LaFarge. Many other faith leaders, including Presbyterian spokesman Eugene Carson Blake and rabbis Uri Miller and Joachim Prinz, spoke. Then, at last, came King’s great moment.

King did not only speak of a dream. He concluded with the profound faith that “we will be able to speed up that day when all of God’s children, black men and white men, Jews and Gentiles, Protestants and Catholics, will be able to join hands and sing in the words of the old Negro spiritual, ‘Free at last! Free at last! Thank God Almighty, we are free at last!’”

The religious left could find no better creed than those very words.

Buoyed by a sense of possibility that accompanied the Civil Rights and Voting Rights Acts passed under Kennedy’s successor, members of the religious left soon transferred their energies to other causes, not least the antiwar movement.

A group calling itself Clergy Concerned About Vietnam, formed in 1965, attracted the leading figures of the nascent religious left, including John C. Bennett, Daniel Berrigan, Eugene Carson Blake, Robert McAfee Brown, Abraham Heschel, Reinhold Niebuhr — and King.

The religious left quickly collapsed at the end of the 1960s. The forces it had helped to unleash proved too strong to contain. Northern whites cooled to the civil rights movement as it began to move beyond the South. Antiwar protests fractured congregations, and so did the early battles of the sexual revolution.

The papal encyclical Humanae Vitae, which reaffirmed traditional teaching on artificial contraception, disappointed many liberal Catholics who, displeased with the pace of reform, left their church. At the same time, membership in mainline Protestant denominations plummeted, impairing these churches and their umbrella organization, the National Council of Churches, in their efforts toward greater social justice.

King’s assassination was not the death knell of the religious left, but the budding conservative reaction already visible in 1968 announced a new landscape in religious activism. That reaction proved to be far more long-lasting — perhaps because of the vacuum opened up by the religious left’s frailties. The religious right has proved its mettle in election after election, as recently as 2016.

In light of his puzzling proximity to evangelical groups, Donald Trump has inspired hopes of a revival of the religious left, as though religious activism were a pendulum. While wringing their hands, some pundits are searching for an ecumenical and liberal movement capable of advancing social justice. They seek the revolutionary language that stirred thousands only several generations ago.

But in the past 50 years, white liberals in particular have lost the ability to set faith in conversation with the world as King effortlessly did (although we should note that Jimmy Carter and Bill Clinton had an ease and conversancy with religious discourse that defeated Democratic presidential candidates did not). Now, to many Americans, faith and liberal values appear mutually exclusive, a legacy of the sexual revolution, the culture wars and the gradual secularization of the Democratic Party.

It is little wonder that we have forgotten King’s religious significance. But we must change that, for King was the prime catalyst of the short-lived but no less remarkable religious left. Casting the watershed achievements of the 1960s not as natural outcomes of a resurgent, secular New Deal liberalism, as some would have it, but as the fruit of new religious alliances might help to point a path forward for liberalism — which has been under siege ever since.