The head cleric of a global religious order, whose followers believe him to be an infallible representative of their god, will on Sunday officially confirm that the late Macedonian-born missionary known by the name of Mother Teresa has successfully seen their deity “face to face”. The cleric, Pope Francis, will officially give Teresa the label of "saint" at a ceremony attended by leaders of diverse nations as well as tens of thousands of members of the ancient order in an event at a tiny theocratic city-state nestled in the heart of Western Europe.

The event is the culmination of a shadowy process that usually takes decades whereby senior members of the sect, known as Roman Catholics, sought to establish that Teresa had entered heaven – a confusing state of existence after death often depicted as paradise but described as a "relationship" with the trio of deities who make up the group's god. While the clerical order has sometimes taken centuries to bestow sainthood on members, the process was speeded up for Teresa, who became famous in her lifetime for running a charitable religious organisation that cared for the sick in the city that was then called Calcutta.

Though she was accused by rationalists of fetishising death and supporting an Indian dictator, Teresa gained international renown for her work at the Missionaries of Charity and was frequently seen in the company of heads of states from around the world. In 1979, Teresa was anointed the winner of a major "peace" prize instituted by the estate of a Swedish arms manufacturer. She used the prize-winning speech to further her religious order’s war against modern science, calling abortion “the worst evil and the greatest enemy of peace”.

Teresa died in 1997. Although the path to becoming a saint – which over the centuries has been plagued with corruption and questionable motives – can normally begin only five years after death, the Roman Catholic Church accelerated the process for Teresa, initiating it in 1999.

The procedure that follows offers a fascinating glimpse of the arcane beliefs that govern this religious order.

Members of the church first had to “investigate” the virtues of Teresa, to affirm that she did indeed adhere to the centuries of complex rules that govern the followers of this religion. Then, once declared a "Servant of God", Teresa’s heroic deeds prompted the church to declare her "Venerable" – after which followers are expected to pray to her for miracles.

The Pope must be able to conclude that the person has indeed seen god face to face, proof of her “beatific vision”, meaning that she can talk directly to the deity and intervene in our world even after death. In Teresa’s case, the head cleric claimed that she had cured a woman of cancer from beyond the grave – even though the woman’s husband and doctors said medicines were responsible. The Pope also said a Brazilian man’s brain tumours were cured by the dead Teresa.

In addition to confirming her presence in heaven, sainthood also means any member of the religious order may commemorate Teresa by arranging a large lunch and prayer or by buying one of the 1.5 million postage stamps released on Friday in her honour.

Inspired by Slate's If It Happened There series, which re-imagines coverage of American events in the manner that the US media writes about the rest of the world.