How to build a saint: Pope Francis is elevating two recent predecessors today - so what does it take to be canonised?

A life of virtue helps. And a miracle or two. Finally, though, the Vatican might be swayed by low politics. Paul Vallely explores the unheavenly business of sainthood

You might think that, since the Catholic Church has more than 10,000 saints, two more might be neither here nor there. But the two men who are to be canonised today are much more than another couple of symbols of sanctity.

In Vatican City's St Peter's Square at 10am this morning, Pope Francis will confer his church's greatest accolade on two of his predecessors as Pope. But the process which has led to the ceremony reveals that there is nothing otherworldly about the business of making saints – and it uncovers some illuminating truths about the Church of which 1.2 billion people across the world are members.

The two new saints will be Pope John Paul II, who died in 2005, and Pope John XXIII, who died in 1963; yet the two are a study in contrasts.

The supporters of the more recent of the pair, the Polish Pope, John Paul II, are clear about the case for his canonisation. The globe-trotting rock-stadium pontiff was the most popular pope of modern times. He visited 129 countries during his 27-year pontificate and some 17 million people travelled to Rome to see him. He was the first pope to visit a synagogue and mosque. He made public apologies for the Crusades and the persecution of Galileo and begged forgiveness for centuries of Christian slander of the Jews. He played a key role in the fall of 20th-century Communism. And he gave dignity to the dying by the public way in which he handled his own protracted final illness. His disciples already call him John Paul the Great.

The trouble is that he also suppressed debate within the Church, censured theologians, ignored a dysfunctional bureaucracy within the Vatican and for decades did little to nothing about the scandal of clerical sex abuse which was first revealed as a large-scale problem in his time.

All that was ignored, however, by his devotees who flocked to Rome after his death, chanting "Santo Subito" ("Make him a saint now") outside the papal apartments.

The pope who followed, Benedict XVI, took the hint and scrapped the rule which usually requires that the track to sainthood cannot begin until at least five years after a candidate's death. It suited Benedict for political reasons. The move consolidated the conservative legacy of the Polish pope, which Benedict wanted to reinforce. Both John Paul II and Benedict XVI worked hard to row back on the changes which had turned the Church upside-down in the 1960s after the revolutionary Second Vatican Council opened up Catholicism to the modern world.

When the latest pope, Francis, was elected, the conveyor belt to canonisation for John Paul II was already unstoppable. That is where the politics got even more complicated. Francis is an enthusiast for the Second Vatican Council, and has declared that there can be "no turning back the clock" on its changes. Indeed, he said, they have not gone far enough.

So Pope Francis decided to mirror the canonisation of John Paul II with that of John XXIII, the smiling, wise-cracking pontiff who launched the Second Vatican revolution and whose admirers call him the Good Pope. It is a very deft piece of political footwork.

So today in Rome a papal odd couple, the Great and the Good, will be linked in a clear attempt to arrest the drift to conservatism which has characterised the Catholic Church for the past three decades.

There has long been a political element to the creation of saints. For the first 1,000 years of Christianity, saints were simply declared by popular acclamation among believers – the original vox populi. Believers voted with their feet by visiting the tombs of dead individuals they regarded as particularly holy.

Local bishops went on to declare such people to be saints – which merely amounted to an affirmation that the venerated individuals must now be with God in heaven. It was a good way, they decided, of giving Christian role models to illiterate believers who had only a limited understanding of the subtlety of abstract theology. From the 4th century on there are accounts of miracles – events contrary to the laws of nature – being credited to saints to whom believers prayed.

It was also a handy way of ensuring that every region got a saint whose remains and relics would be a focus for pilgrims bringing donations, and thereby economic and political power, to a bishop's cathedral.

But in the high Middle Ages, the Church authorities in Rome decided it would be better if they took control of the business, to ensure that everyone got the right idea of what it meant to live out the theological virtues of faith, hope and charity and the moral virtues of wisdom, prudence, justice, temperance and courage.

In 1170, Pope Alexander III issued a decree saying that only the pontiff could say who was to be saint. In 1234, Pope Gregory IX established procedures to investigate the life of a candidate and any miracles attributed to them. In 1588, Pope Sixtus V entrusted the process to a body now known as the Congregation for the Causes of Saints. The rules were constantly tightened by Rome, which also set up rules for the authentification of sacred relics that proliferated preposterously in the medieval era. There was said to be enough wood in relics from the True Cross to build a galleon.

There have been two major reforms in recent years. In the 1960s, Pope Paul VI ordered a review of the Roman canon of saints, which weeded out many found to be legends rather than historic facts. St Christopher, the patron saint of travellers – who legendarily carried the Christ-child across a river but found himself unable to manage since the boy carried the weight of the world on his shoulders – was one such who went.

Then, in 1983, John Paul II made sweeping changes to the canonisation process. He abolished the Devil's Advocate, a canon lawyer tasked with making the case against a candidate for sainthood. The Pope's intention was to enable himself to declare more saints from the ranks of ordinary people among a wider range of nationalities to create more representative exemplars for the average person in the pew. He made the whole process faster and simpler.

As a result, Pope John Paul II then declared more saints than all the popes in the half- millennium before him. He created 483 new saints – compared with just 98 from all his 20th- century predecessors. He also beatified 1,300 more, giving them the precursor status to being a full saint (see box, below). One of the most select clubs known to humankind thus became a lot less exclusive. It also became a little more geographically representative, with figures from Africa, Asia and Latin America – where the church is growing fast – being added to the overwhelmingly European canon of saints.

Saint-making has always been political. The Church of England does not do saints but sections of it have canonised King Charles I of England, a gesture which may have been more of an institutional antidote to regicide than a recognition of personal holiness. And in the Orthodox churches – where the Eastern, Oriental and Russian branches have made large numbers of saints independently of one another – the semi-autonomous Russian Orthodox Church Abroad has canonised Tsar Nicholas II and the rest of the Romanovs who were murdered by the Bolsheviks in Yekaterinburg during the Russian Revolution in 1918.

Political lobbying is part of the process. The conservative Opus Dei group, favoured by Pope John Paul II, successfully pressed him to canonise the order's dubious founder, Josemaría Escriva, who was made a saint in record time. By contrast, the process to canonise Oscar Romero – the archbishop murdered at his altar in 1980 by right-wing death squads in El Salvador – was blocked under John Paul II and Benedict XVI because his cause was backed by left-wingers of whom the popes were suspicious.

Pope John Paul II also used sainthood to promote the issues which should preoccupy the church. Among those he canonised was an Italian paediatrician, Gianna Beretta Molla, who died in 1962, aged 39, days after giving birth to her fourth child. During her pregnancy, doctors had found a tumour in her uterus and told her she would die if she did not have it removed – which would have had the side-effect of killing her unborn baby in the process. She refused and died. Saint Gianna was subsequently praised by John Paul II for her "extreme sacrifice".

Miracles are also central to the business of being made a saint. Ordinary Catholics can pray to a dead person they regard as holy and ask them to intercede with God to perform a miracle on their behalf. If the miracle materialises, the Church argues, that must prove the dead person is in heaven. To investigate claims of miraculous cures, the Congregation for the Causes of Saints in Rome employs teams of doctors to check proposed cases.

Not all of these doctors are Catholics and some are asked to make medical judgements without being told why. Canadian professor Dr Jacalyn Duffin, an atheist, thought she was checking fatal leukaemia cells for a post-mortem and was staggered to discover they belonged to someone who was alive, having undergone an inexplicable cure. Dr Duffin is still an atheist but now says: "I believe in miracles – wondrous things that happen for which we can find no scientific explanation."

The arrival of Pope Francis has brought a shift of emphasis. True, early on he canonised 813 individuals who were martyred at Otranto in southern Italy after refusing to convert to Islam in 1480. But those saints were already in the pipeline when he became Pope; the announcement had been made by Pope Benedict, who had rather overshadowed the news by declaring at the ceremony that he was to become the first pope to resign for 600 years.

Francis showed his impatience with the old procedures by unilaterally waiving the need for a second miracle, in order to push through the sainthood of Pope John XXIII on the same day as John Paul II to bridge the old divide between progressive and conservative Catholics. What's more, he has lifted the block on Oscar Romero becoming a saint. But it seems unlikely from all the other signs he has given that Pope Francis will be creating huge rafts of new saints as his two predecessors have done.

Nor should he. There is something faintly unseemly, and distinctly political, about recently dead popes being fast-tracked to sanctity. Elsewhere, the Church is fond of saying that it likes to think not in years but in centuries. Popes should not be declared saints until at least a few hundred years have been allowed to elapse to let contemporary controversies settle into the dust of history.

'Pope Francis: Untying the Knots', by Paul Vallely, is published by Bloomsbury, priced £12.99

Canon fodder: The saintly process

10,000

The Vatican's Congregation for the Causes of Saints believes there are at least 10,000 saints.

483

Pope John Paul II created 483 new saints – compared with just 98 made by all his 20th-century predecessors.

British saints

Saint: Thomas Becket Canonised in 1173.

On his way: John Henry Newman The most recent British beatification, Newman left the Anglican Communion to become a Catholic in the 19th century.

Not a saint: Henry VI Unsuccessfully proposed for canonisation, despite the attribution of several miracles.

The great and the good

Pope John Paul II (1978-2005) and Pope John XXIII (1958-1963) will be canonised today.

4 steps to heaven

Step 1 - Once you have been dead for five years someone can propose you become a saint. Your local bishop will check that there is no huge scandal in your life and the "purity of doctrine" in your writings. Witnesses are called. A report is sent to Rome.

Step 2 - The Congregation for the Causes of Saints in Rome will check that you have lived a life of "heroic virtue". If satisfied, it will ask the Pope to declare you Venerable.

Step 3 - Next you have to perform an indisputable miracle from beyond the grave. This is an "immediate, complete and spontaneous" cure of a serious disease or condition which medical science cannot explain or refute. You do this to someone who has prayed to you. If you were a martyr you can skip this step. Once the miracle is verified, you are beatified and called Blessed.

Step 4 - Another miracle is needed for canonisation. Again you cure someone who has prayed to you to intercede with God for them. This proves you are in heaven. Once the miracle is certified, a Canonisation Mass is held, you are given a Feast Day and thereafter called Saint. The decision is infallible and irrevocable.