Martin Luther and the Rev. Martin Luther King Jr.  (AP Photos)

Christians worldwide are celebrating the 500th anniversary Tuesday of the Protestant Reformation. Martin Luther, in posting his 95 Theses on the door of a church in Wittenberg, Germany, challenged the church hierarchy of his day, calling Christians back to the Bible and to salvation through faith alone. Luther was fiery, bold and prophetic. And it’s no coincidence that he’s the namesake of the most significant religious figure in U.S. history: the Rev. Martin Luther King Jr.

Few people know the story of the connection between the two reformers. What they share in common is far greater than a name.

The story begins in 1934, when King’s father traveled to Berlin to attend the Fifth Baptist World Alliance Congress. There, he and 29 other black ministers helped racially integrate the Congress in the face of a “color ban.” They also condemned the rising anti-Semitism they saw in Nazi Germany.

While in Berlin, Michael King Sr. (as he was then known) learned about Luther’s denunciations against the injustices of the medieval penitential system. Luther’s struggle resonated with King, who wondered what such boldness might mean for racial injustice in the United States.

Luther’s legacy left such an impression on King that he changed his name, and the name of his then-5-year-old son, to Martin Luther King. Although King Sr. would go on to make his own courageous stand for social justice, his son’s life and legacy was destined to more closely mirror that of the monk from Germany.

Both Luther and King Jr. publicly protested the exploitation of the poor. Luther’s objections to the Catholic Church’s teachings on justification (how people are saved) came to a head over indulgences. At the time, indulgences could be purchased to grant remission of penalties for sins. Indulgences became a means of widespread economic exploitation, preying on the poor’s fear of punishment in the afterlife.

On All Saints Eve of 1517, Luther nailed his 95 Theses to the Wittenberg church door to denounce the sale of indulgences and invite church leaders to a public debate. This was a calculated public protest. It was meant to dramatize the suffering of the marginalized in a way that the powerful could not ignore.

Luther’s 43rd thesis states, “Christians are to be taught that he who gives to the poor or lends to the needy does a better deed than he who buys indulgences.” Even more provocative was Luther’s 45th thesis: “Christians should be taught, he who sees his neighbor in distress and, nevertheless, buys indulgence is not partaking in the Pope’s pardons, but in the wrath of God.” Luther protested both doctrinal errors and the social exploitation that they led to. Luther’s heirs are known as Protestants today because his movement was so centered on protest.

Nearly 450 years later, King would likewise use public protest to confront the social devastation of false doctrine.

The entire system of segregation in the U.S. South was built on false doctrine: namely, black inferiority. Historian Rebecca Goetz traces the idea to Anglican ministers in Colonial Virginia, who crafted the idea of “hereditary heathenism.” It was the belief that enslaved Africans and indigenous people could not become Christians. This belief, writes Goetz, “laid the foundations for an emergent idea of race and an ideology of racism” in the United States.

King’s roots at Ebenezer Baptist Church in Atlanta taught him to recognize the spiritual and theological roots of racism. Later, his extensive college studies gave him the theological and philosophical categories he needed to expose it. When King arrived in Montgomery, Ala., in 1953, he immediately recognized the religious dimensions of the racial climate. “The racial peace which had existed in Montgomery was not a Christian peace,” he wrote. “It was a pagan peace, and it had been bought at too great a price.”

King turned to public protest to expose this “pagan peace” and confront the economic and legal systems that perpetuated it. When he and other members of the Montgomery Improvement Association organized a bus boycott in 1955, they knew they were igniting a public debate that could dismantle the entire apparatus of systemic racism.

Significantly, both Martin Luther and his namesake emphasized God’s love as the centerpiece of social engagement. Throughout his life, Luther maintained a commitment to divine love as the guiding principle to social action. Like Luther, King also emphasized divine love as the ground of social engagement.

King centralized the cross of Christ as the particular revelation of God’s love that empowers and guides social action. When he was arrested and unjustly tried, Christ did not respond with retaliation or passivity. Rather, he responded with self-giving nonviolent action. This redemptive pattern guided and empowered the entire nonviolent movement.

For King, the cross and resurrection of Christ proved that God uses faith-filled engagement with suffering in transformative ways. The cross shows that love will have the final say over injustice. So as freedom fighters committed themselves to nonviolence in the face of billy clubs and fire hoses, civil rights leaders did so believing that “unearned suffering is redemptive.” God’s love is the only power that can overcome hatred. As King demonstrated, God uses social engagement with suffering to transform the hearts and minds of a nation.

In his own context, Martin Luther could never have imagined a Martin Luther King Jr. But the two are not as different as it may appear. On one hand, Luther (and the Protestant Reformation) had greater social motivation and implications than people often realize. And on the other, King and the civil rights movement of the 1950s and ’60s had greater theological motivations and implications than people often acknowledge.

Those of us who embrace both men as part of our religious heritage have an opportunity to appreciate public protest as part of the legacy of the Protestant Reformation. Perhaps the young activists who are marching, kneeling and praying in defense of black life have a more significant stake in the legacy of the Reformation than we know. And perhaps those who claim Luther’s heritage have a more significant stake in the defense of black lives.

Mika Edmondson is the pastor of New City Fellowship in Grand Rapids, Mich., and the author of “The Power of Unearned Suffering,” a book on King’s theology of suffering.