The Bible was written by believers in capital punishment. As recently as 2001, Avery Dulles, an American Jesuit scholar, noted that “The Mosaic Law specifies no less than thirty-six capital offenses calling for execution by stoning, burning, decapitation, or strangulation. Included in the list are idolatry, magic, blasphemy, violation of the sabbath, murder, adultery, bestiality, pederasty, and incest.” This list is not just of antiquarian interest: Saudi Arabia still beheads women for adultery and “sorcery”; Iran hangs people for blasphemy. But all the historically Christian countries of the west bar the US have turned their backs decisively on the death penalty, and so have most of the churches within them. The most important of these is the Catholic church, which also supplies a majority of the justices on the US supreme court. Pope John Paul II, in other contexts a champion of reaction, taught that the death penalty had no practical application in the modern world, even though it was theoretically permissible. Pope Francis has now hardened this position. He has changed the catechism to say that “the death penalty is inadmissible because it is an attack on the inviolability and dignity of the person”. This is no longer his personal opinion, but something that Catholics ought to believe; he adds that the church should work for the abolition of the death penalty everywhere.

This is more than a matter of concern to Catholics. He has touched an issue that is a political live wire in several countries where the church is an important political force. In the US, the pope’s decision has been greeted with rage and anguish on the Catholic right; on the other hand it will give heart to campaigners against the death penalty, and some of the most prominent of these are also Catholics. In Britain it can stand as a rebuke to the efforts of the May government to ship jihadis to the US without seeking assurances that they would not face execution.

While Amnesty International says the global trend towards abolition continues, some countries have reintroduced capital punishment or revived its use. In the majority-Catholic Philippines, Rodrigo Duterte anticipated his pledge to bring it back with a government-sanctioned campaign of extra-judicial killing against those suspected, or merely denounced, as drug dealers which has killed at least 4,000 people and possibly three times as many.

Though the legislative tide is clearly running against the death penalty, attitudes towards it track one of the most important fault lines in contemporary politics. It is one of the litmus tests of social conservatism. The death penalty is the ultimate assertion of the primacy of collective interests over those of the individual. And in most of Europe the mainstream churches were for years among its strongest supporters: the 39 Articles of the Church of England include a commitment to the death penalty, inserted to defy the radical Protestants of the 16th century who doubted any state’s right to take life.

So how did the Catholic church, which is among other things the world oldest continually functioning bureaucracy, come to reverse its doctrine over a period of no more than 50 years – a blink of an eye as the Vatican counts? The secret is to claim that doctrine never changes, while transforming its content when necessary. The ability to define what is “unchanging” and what is merely “development” is necessary to give apparently unchanging institutions the flexibility they need to change and to survive. Inch by inch, the supertanker turns until it is facing in the right direction.