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This article originally appeared in The Guardian, and has been reproduced with permission

Mother Teresa once went to a cash-and-carry-in London. She filled a huge trolley with food for her hostel for homeless men in Waterloo. At the till she was told the total was more than £500. “It’s for the poor,” she said. “Very admirable,” said the store’s owner, repeating the total. “No, you don’t understand,” she said. “It’s for the poor.”

The shopkeeper told the nun that it was she who did not understand: she still had to pay. To the embarrassment of the English volunteer who had driven her to the shop, a standoff ensued, with the nun and the owner reiterating their positions over and over. Eventually the customer waiting behind with his own trolley told the shopkeeper: “It’s all right, I’ll pay for hers.” “See?” the wily nun said to the volunteer as they loaded his boot, “I told you God would provide.”

Next week, on the 19th anniversary of her death, the Vatican will declare Mother Teresa to be Saint Teresa of Kolkata. It is a controversial canonisation.

To her admirers, the fruits of her holiness are evident, in her legacy of homes for the dying, homeless hostels, soup kitchens, leprosy clinics, HIV/Aids hospices, orphanages, schools, mobile dispensaries, mother and baby clinics, and centres for drug addicts and alcoholics in 133 countries. They are run by the 4,500 sisters in the Missionaries of Charity order, which she founded in 1950 to help those she called “the poorest of the poor”. Her work for the disadvantaged won her the Nobel peace prize. Malcolm Muggeridge, the man whose 1969 film set the Albanian nun on the road to becoming an international household name, called what she did, in the title of his 1971 book, Something Beautiful for God.

It is a far from universally accepted verdict. The most formidable of her critics was another British journalist, Christopher Hitchens, who in 1994 made a film called Hell’s Angel. It claimed that Mother Teresa treated the symptoms of poverty while ignoring the causes. She took money from distasteful political figures and rich fraudsters, and didn’t publish any accounts. Her Catholic opposition to abortion and contraception made her a religious fundamentalist. Her Kolkata home for the dying had poor medical standards. It all constituted, Hitchens railed, a “cult of death and suffering”.

Should all that disqualify her from being a saint? Hitchens’s critique is polemical – his 1995 book on her is framed with attacks on religion in general – but it airs concerns raised by an Indian doctor, Aroup Chatterjee. It has interviews with volunteers from the Kolkata Home for the Dying Destitutes, who spoke of needles reused without sterilising them, too few drips, and little pain control beyond aspirin. The Lancet visited in 1994, and said the home failed to distinguish between dying patients and those who could be cured.

All this stemmed, critics said, from Mother Teresa’s archaic religious attitude to suffering, which she saw as “beautiful” because it enabled poor people to “share in the passion of Christ” – though that did not prevent her from being treated in expensive medical facilities when she herself was ill.

It was not a view all the dying shared. When she told one man “you are suffering like Christ on the cross, so Jesus must be kissing you,” he replied: “Then please tell him to stop kissing me.” Mother Teresa was unrepentant, insisting that a home for the dying was not a hospital. “We are not nurses, we are not doctors, we are not teachers, we are not social workers,” she said: “We are religious.”

Certainly, Mother Teresa embraced an “ostentatious anti-materialism” that bordered on primitivism. In her San Francisco convent, she threw out all the mattresses, carpets, curtains and sofas, arguing that comfort corrupted. In the Bronx she refused to open a home for the poor when the local authorities insisted it had to have an elevator. In Rome she reprimanded her sisters for canning a glut of tomatoes, saying it revealed a lack of trust in God.

Yet many found that severity attractive. From the 60s onward she was repeatedly named in polls of the world’s most admired figures. Her compassion for the poor, rejection of consumerism and countercultural lifestyle resonated with the idealism of the times. She became part of the collective imagination as a casual synonym for goodness: “Who do you think you are? Mother Teresa?”

But the two sides of the ledger are not incompatible. In war-torn Beirut, ignoring warnings of extreme danger, she crossed the green line to rescue mentally and physically disabled children trapped in a hospital under fire. One Red Cross worker said: “She saw the problem, fell to her knees and prayed for a few seconds, and then she was rattling off a list of supplies she needed.” She was “like a cross between a military commander and Saint Francis”. Providence and planning to her were not alternatives.

In Ethiopia, travelling with a minister from the Stalinist Mengistu regime, she made small talk. But, when the world’s press were present, she asked about a large building they had passed. It would make a good orphanage she said. It was a government ministry, he replied. But, said the crafty nun, hadn’t the ministry just moved out? Wasn’t it now empty? Well, yes, but … The minister blustered, but she countered his every response. Every question she asked, she already knew the answer to. She got her orphanage. She used the same techniques everywhere. When she first met the owner of the Daily Mirror, Robert Maxwell, she asked for a donation. When he offered a measly amount she declined it, and said she would go to the Sun instead. He paid up.

Her defenders said she was not cosying up to dodgy rich people, but working in the world as she found it. Bad money could be redeemed by putting it to good use. Her critics called her disingenuous, but she insisted some good was always to be found in every person and any situation. Jesus mixed with disreputable characters. A good act might be a redemptive doorway for a bad person.

This combination of personal faith, unremitting dedication, clarity of focus, PR savvy, organisational genius and constant travel made her, in the words of former UN secretary general Javier Pérez de Cuéllar, “the most powerful woman in the world”.A saint is not a perfect person but a holy one.

One of the qualities the Catholic church requires to canonise someone is that they have “heroic virtue”. In the past the church allowed decades, even centuries, to pass before declaring someone a saint. With the passing of time a candidate’s foibles and weaknesses faded from common memory, leaving only their towering heroic virtue in the general mind. But, since Pope John Paul II, the fashion has been to accelerate the canonisation process. The Catholic church has made a serious mistake on this. Mother Teresa may merit sainthood, but that is a judgment it would be better to make a century from now.

Saints can be signs of contradiction. During the Ethiopian famine of 1985, I visited three refugee camps near Alomata. Grain was being distributed in the first, amid much shouting and pushing. Triage doctors in the second were sorting skeletal people into those in need of treatment, those not yet quite ill enough to warrant it, and those beyond help. The soundtrack to the process was the piercing cries of pleading mothers.

The third camp was run by Mother Teresa’s nuns, to care for those deemed too sick for treatment in the second camp. It was an oasis of peace and serenity, where nuns dropped water on to the cracked lips of the dying, or simply sat and held their hands. “Do small things with great love,” Mother Teresa had instructed them. That remains my deepest memory of her.

Paul Vallely writes on religion, ethics and development in Africa