Pope Francis set the cat among the pigeons last week, telling an audience convened to mark the 25th anniversary of the Catechism of the Catholic Church that “the death penalty is an inhumane measure … regardless of how it is carried out” and must be regarded as “contrary to the Gospel.”

That got everyone’s attention.

It isn’t news that Catholic leaders oppose the death penalty. The U.S. Conference of Catholic Bishops has for years actively worked against capital punishment. Pope John Paul II denounced it often, most famously in a 1995 encyclical, “Evangelium Vitae.” And Francis himself has called for the abolition of capital punishment. He insisted last year that it is incumbent on “all Christians and men of good will” to end executions, even for murder.

But the pope’s recent remarks weren’t just more of the same. In pronouncing the death penalty “contrary to the Gospel,” Francis appears to be saying something that none of his predecessors ever said, namely, that one cannot be a faithful Catholic and support capital punishment. That has never been church doctrine. On the contrary: The most eminent popes, theologians, and church fathers have for centuries affirmed the legitimacy of the death penalty in appropriate cases, while acknowledging that faithful Catholics may disagree about what “appropriate” means.

John Paul II crusaded openly against the death penalty, going so far as to intercede with U.S. governors to grant clemency to killers on death row. But he never suggested that the death penalty was always and everywhere contrary to God’s law. He couldn’t have. The Bible itself explicitly proclaims otherwise, starting in Genesis with God’s injunction after the Flood. After blessing Noah and his family (“Be fruitful and multiply, and fill the earth”), God forbids mankind to commit murder — and warns that the punishment for murder is death: “Whoever sheds the blood of man, by man shall his blood be shed, for God made man in his own image.”

There is sanction for the death penalty in the New Testament, in the writings of St. Augustine and Thomas Aquinas, in the instruction of numerous popes. For the better part of two millennia, Catholic doctrine has upheld the lawfulness of the death penalty. Its legitimacy is acknowledged in the catechism promulgated by John Paul II 25 years ago — the very document that last week’s audience in the Vatican gathered to commemorate.

“The traditional teaching of the Church does not exclude recourse to the death penalty,” the catechism teaches, “if this is the only possible way of effectively defending human lives.” Such cases will be “very rare, if not practically non-existent.”

But if Pope Francis’s words are to be taken at face value, that isn’t enough. He wants the church to renounce a truth it has affirmed through its entire existence, and henceforth to profess that the death penalty is and always has been immoral. That would be an astonishing precedent, and would cause untold upheaval.

“For if the church has been that wrong for that long about something that serious,” asks Edward Feser, a professor of philosophy and co-author of a well-timed new book on Catholicism and capital punishment, “why should we trust anything else she teaches?”

To nonbelievers and non-Catholics, the whole subject may seem little more than Vatican shop talk. Legislators, not popes, write our criminal codes. If Francis wants to change church doctrine, why should outsiders care?

This is why: Because the death penalty is a tool of justice that no decent society should unequivocally renounce, and because more innocents die when the worst murderers know that they face no greater risk than prison. The Catholic church at its best has been a mighty upholder of human dignity. But when remorseless killers have a greater right to life than their victims, human dignity is trampled into the mud. Surely that isn’t the legacy Pope Francis seeks.

Jeff Jacoby is a columnist for The Boston Globe.