A young man clad in white robes leads a dozen others across a barren landscape towards a modern town. In a supermarket, he stamps on tomatoes grown by badly paid workers in appalling conditions. "We just want to say," he declares through a loud hailer to a passionate, banner-waving crowd: "'I have my dignity too!'" Finally, he appears to walk on water.

These are scenes from The New Gospel, a radical new film by the Swiss-born, Belgium-based director Milo Rau. In it, he sets out to answer a series of questions: what would Jesus preach in the 21st Century? What principles would he defend? Who exactly would he stand up for?

The film was shot mainly in Matera, a southern Italian town known for its dramatic, rocky surroundings, including a honeycomb of ancient cave dwellings. It had previously been used as a location for Jerusalem in two memorable retellings of the Easter story, Pier Paolo Pasolini's The Gospel According to St Matthew and Mel Gibson's The Passion of the Christ.

Rau's initial idea was simply to make a film using actors who had appeared in those movies. But he changed his mind when he arrived in Matera and found African immigrants working on farms for as little as €3.50 an hour and living in shantytowns without electricity or running water. "I decided to not only make a Jesus film," he says, "but also to include the reality of their fight for dignity, which is also what Jesus stands for."

Rau likes to cast activists and ordinary people alongside professional actors in his films. To play Jesus, he chose Yvan Sagnet, an immigrant from Cameroon, who has worked on exploitative farms himself and now campaigns on behalf of their labour forces. Most of Jesus's disciples are played by migrant workers.

"For us, Jesus was a prophet and an activist for justice," says Sagnet. "He was a union leader; he fought." In the film, a boat carrying Jesus and his disciples is welcomed by the leader of a charity that rescues shipwrecked migrants. Christ's entry into Jerusalem becomes a protest march.

But there is more to The New Gospel than a biblical narrative. It is also a documentary about the living conditions of the migrant workers, and about the making of the movie itself, with footage of the auditions and rehearsals.

Alongside the filming, Rau organised a political campaign called The Revolt of Dignity. It has a manifesto drafted by the migrants playing Jesus's followers, and includes public debates with local officials on subjects such as racism and the difficulty of obtaining legal immigration status.

Rau was inspired by one Bible passage in particular: "Jesus says: 'Do not think that I have come to abolish the law or the prophets: I have not come to abolish them but to fulfil them.' Everything we want for the dignity of these people is in European and Italian law. This situation is illegal."

In fact, says Yves Sagnet, "The film is the beginning, not the end."

Some say, yes: Milo Rau's decision to present him as one makes complete sense. Jesus aligned himself with the poorest and most rejected people in society, and there is no doubt that migrants occupy that position today. There are so many of them in the world - over 280 million according to the United Nations - that he could not conceivably ignore them.

Others point out that although Jesus came from a poor family, he was a recognised member of the Jewish community. This gave him a voice in it, even if what he said was not what others wanted to hear. But a voice is one thing migrants today do not have. It would have made more sense for Rau to present Jesus as an Italian aid worker who stands up for them.

Matera - Situated in the heel of Italy, it has an official population of approximately 60,000 people.

Cave dwellings - Known as the Sassi, these are thought to date from the Paleolithic era. They were still used as houses up until the 1950s.

Mel Gibson - An Australian actor and director best known for starring in the Mad Max series of films.

Cameroon - A West African country with a population of over 100 ethnic groups. Its president, Paul Biya, has held power for 40 years.

Shipwrecked migrants - The charity is called Mediterranea Saving Humans. It is thought that around 1,000 migrants died while trying to cross the Mediterranean in 2020.