For nearly two millennia the Catholic Church read "Thou Shalt Not Kill" as a prohibition of murder, not a ban on all killing. The Hebrew is clear: lo tirtzach means the unlawful taking of innocent life. Jewish tradition built an entire legal framework around that distinction. Christian thinkers understood it too. Augustine and later Aquinas both drew sharp lines between murder and forms of killing that might be justified – in war, in self-defense, or in judicial execution.
Aquinas went further in a way that today sounds shocking. In the Summa, he argued that because society justly executed counterfeiters for undermining trust in the common good, it was all the more just to execute heretics, who endangered eternal salvation. His analogy only made sense because everyone assumed that counterfeiters deserved death – an assumption woven into medieval law. The Church never applied the commandment against “killing” to such cases. It was always understood as murder.
From the thirteenth century onward the Church cooperated with secular rulers in the suppression and execution of heretics, notably during the Inquisition. This was not treated as a violation of the commandment but as a necessary defense of truth and society. Even into the early modern period, Catholic and Protestant authorities alike justified executions for heresy. The distinction between murder and other forms of killing was taken for granted.
That began to change in the 19th century. Enlightenment thinkers challenged the ubiquity of the death penalty. States gradually stopped executing people for crimes like counterfeiting. The Church, still committed to just war and judicial punishment in principle, began to shift under the pressures of modern warfare. Nuclear weapons, world wars, and totalitarian massacres made the old just war categories look dangerously inadequate.
Vatican II condemned indiscriminate attacks, declaring the destruction of entire cities to be a crime against God and man. The Catechism maintained the legitimacy of defense, but the tone grew more cautious. John XXIII and Paul VI urged disarmament and development. John Paul II went further, declaring war itself “always a defeat for humanity,” and suggesting that modern wars almost never meet the just war criteria. Francis carried the trajectory forward, declaring the death penalty inadmissible and adopting a near-pacifist stance in public appeals.
Through all of this the Church retained the old English formula “Thou shalt not kill” in its catechetical headings, while continuing to teach that what was forbidden was murder. Other Christian traditions moved their translations toward accuracy – “murder” rather than “kill.” The Catholic Church knew the difference but kept the older form for continuity and resonance.
That is what makes the recent papal tweet so significant.
For the first time, the commandment itself was invoked directly in opposition to a specific war, and in the blunt, imprecise English of “Thou shalt not kill.” Popes denounced World War I and World War II, opposed Vietnam, criticized the Gulf War and the Iraq War, prayed for peace in Syria and Ukraine – but they did not wield “Thou shalt not kill,” itself as their banner. The choice to do so now, in connection with Gaza, is deliberate.I express my profound closeness to the Palestinian people in Gaza, who continue to live in fear and to survive in unacceptable conditions, forced once again from their own lands. Before Almighty God, who commanded “Thou shalt not kill,” and throughout human history, every person always has an inviolable dignity, to be respected and upheld. I renew my appeal for a ceasefire, the release of hostages, and a negotiated diplomatic solution, in full respect of international humanitarian law. I invite everyone to join my heartfelt prayer that a dawn of peace and justice may soon arise.
— Pope Leo XIV (@Pontifex) September 17, 2025
The effect of the language is unmistakable. By choosing “kill,” the Pope erases the long-standing moral distinction and frames Israel’s military actions as a violation of God’s law. He is not just lamenting civilian deaths, or warning against indiscriminate bombing. He is implying that Israel is deliberately killing innocents, and doing so under the most absolute prohibition in the Bible.
This is deeply troubling given the Church’s history. For centuries Christians accused Jews of violating this commandment in the ultimate way, branding them as “Christ-killers.” Sermons and pogroms turned that charge into violence. Vatican II repudiated the deicide slander and worked to rebuild relations. But the memory of antisemitism is not erased. When a Pope knows the difference between murder and killing, and when the Church itself has preserved that distinction for two millennia, the decision to reach for the broader “kill” – and to do so for the first time in the context of Israel’s defense – cannot be dismissed as careless wording.
Statements like this are reviewed, drafted, and weighed. They are not accidents. Leo's native language is English. Which means that in its modern evolution from just war to near pacifism, the Church has now taken an additional step – turning the commandment itself into a weapon of accusation, and directing it first and foremost against Israel which is going to unprecedented lengths to avoid civilian deaths while trying to defeat Hamas.
Given the history, that choice is not only theologically imprecise. It risks reviving the very old prejudice the Church has worked so hard to bury.
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