Posthumous portrait of Martin Luther as an Augustinian monk (Workshop of Lucas Cranach the Elder, public domain)

Five hundred years ago tomorrow — on Oct. 31, 1517 — an Augustinian monk named Martin Luther is said to have nailed his “95 Theses” to the door of Castle Church in Wittenberg, Germany, the university town where he lived and taught. Whether or not he actually hammered them to the church doors, he did mail them to his archbishop and thus formally challenged the Roman Catholic Church, which dominated Europe at the time.

This act of public protest is traditionally seen as the launching point of the Reformation, which eventually split the church into numerous denominations.

The main grievance Luther aired that day was that the church was making money by selling indulgences, or guarantees to forgive a dead person’s sins and thus help him or her move from purgatory to heaven. He was right — it was a corrupt scam — but church authorities were too proud to admit that at the time. Pope Leo X ordered Luther to recant, he refused, and eventually the pope excommunicated him and the holy Roman emperor named him an outlaw.

Jesus, his apostles and evangelists such as St. Paul founded the church on the margins of society. They decried “powers and principalities,” preaching selflessness and suffering persecution for their beliefs until the year 313, when Roman emperor Constantine proclaimed tolerance for Christianity. By Luther’s time, the church of Rome had become immensely powerful, and with power comes corruption.

If the church had retained the humility of its early days, it would have recognized the criticisms as legitimate and reformed itself. Instead, it became splintered into numerous denominations. Pride fed the Reformation.

So did new technology that shifted power to the people and helped them spread Luther’s ideas. The printing press, invented by fellow German Johannes Gutenberg around 1440, had become common by 1517, and Luther’s Theses were immediately printed and widely distributed. Luther soon learned to maximize the power of the press by writing follow-ups in the vernacular language (German rather than Latin, the language of the church) by keeping them short and by accompanying them with pictures.

Luther preached several things that were contrary to church doctrine at the time. He believed salvation comes from faith alone and cannot be earned by good works. He believed in a priesthood of all believers and took issue with clericalism. He thought more people should read the Bible and thus translated it into the vernacular; in doing so, he essentially had to invent a unified German language readable across various regional dialects.

The Roman Catholic Church now acknowledges all these things, as well as that the sale of indulgences was sinful. These days, both Lutheran and Catholic leaders say their churches ought to do penance for rupturing Christianity.

“We’ve had to say that breaking up the Western church was not a gift to the church,” Elizabeth Eaton, presiding bishop of the Evangelical Lutheran Church in America, recently told National Public Radio.

Lutherans also apologize for Luther’s vicious antisemitism. Later in life, after he realized he was unable to convert Jews, he called for his followers to kill them, burn their synagogues, smash their homes and seize their property. Such was his influence that Germany became a hotbed of antisemitism. Scholars debate how much the Nazis borrowed from Luther.

Bad acts have lasting consequences. The need for penance continues.

Now Lutherans and Catholics are closer than they have been in 500 years, as evidenced by an ecumenical service held in Sweden, led by Pope Francis. The denominations don’t agree on everything, such as letting priests marry or performing same-sex marriages, but there is reason to hope for real, substantial reconciliation.

We don’t realistically expect all Protestants and Catholics to reunite anytime soon, but we do hope this anniversary will get them to think hard about why they stay apart. They are all one family of faith — all parts of the “body of Christ,” to quote St. Paul. The things that keep them apart are human, while the things they share in common are divine.