Pope Francis, who has often appeared to revel in confounding and surprising others, is at it again.

Many times over the years, he has seemed to suggest he is slowing down, only to ramp up his activities again.

At nearly 88 years old, he has a knee ailment that impairs mobility, abdominal problems caused by diverticulitis and is vulnerable to respiratory issues owing to the removal of most of one of his lungs.

Last autumn, the Pope said his health problems meant that foreign travel had become difficult. Soon after, when he cancelled a trip to the UAE, it led to heightened speculation about the extent of his medical difficulties.

But that was then.

Now, he is in the middle of the longest foreign visit of his 11-and-a-half year papacy. It has been one packed with engagements, and as well as Timor-Leste it involves three countries – Indonesia, Papua New Guinea and Singapore – in which Catholics are a minority.

So why is the Pope travelling so extensively and so far from home?

His supporters say his passion drives him.

“He obviously has an enormous amount of stamina and that is driven by his absolute passion for mission,” says Father Anthony Chantry, the UK director of the Pope’s mission charity Missio, who has just been appointed to the Vatican administration’s evangelisation department.

“He talks about all of us having a tireless mission to reach out to others, to set an example.”

Christian “mission” is something that has evolved over the centuries. It is still about spreading the gospel but now the stated aim is focused on social justice and charitable endeavours.

Throughout his trip Pope Francis will meet missionaries, including a group from Argentina now based in Papua New Guinea. But on numerous trips around Asia including this one, he also skirts close to China, a country with deep suspicions about the Church, its mission and its motives.

The Pope has frequently emphasised the importance of evangelisation for every Catholic. Yet in many parts of the world, it is still hard to separate ideas of “missionaries” and “evangelisation” from notions of European colonisation.

As the number of Catholics in Europe declines, is “mission” and “evangelising” in Asia and Africa now about Church expansion in those parts of the world?

“I think what he is preaching is the Gospel of love that will do no one any harm. He's not trying to drum up support for the Church, that's not what evangelisation is about,” says Father Anthony.

“It isn't to be equated with proselytising, that is not what we have done for a long time. That is not the agenda of the Holy Father and not the agenda of the Church. What we do is we share and we help people in any way we can, regardless of their faith or not having any faith.”

Father Anthony says being a Christian missionary in the modern day, for which Pope Francis is setting an example, is about doing good work and listening, but sometimes, “where necessary”, also challenging ideas.

“We believe God will do the rest, and if that leads to people accepting Jesus Christ, that's great. And if it helps people to appreciate their own spirituality – their own culture – more, then I think that is another success.”

Certainly the Pope has long talked of interfaith harmony and respect for other faiths. One of the most enduring images of his current trip will be his kissing the hand of the Grand Imam of the Istiqlal Mosque in Jakarta and holding it to his cheek.

He was warmly welcomed by people coming out to see him in the most populous Muslim-majority country in the world.

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Pope Francis will end his marathon trip in Singapore, a country where around three-quarters of the population is ethnic Chinese, but also where the Catholic minority is heavily involved in missionary work in poorer areas.

For centuries now, Singapore has been something of a strategic regional hub for the Catholic Church, and what Pope Francis says and does there is likely to be closely watched in China, not least by the Catholics living there. It is hard to get a true picture of numbers, but estimates suggest around 12 million.

The lack of clarity over numbers is partly because China’s Catholics have been split between the official Catholic Church in China and an underground church loyal to the Vatican that evolved under communism.

In trying to unite the two groups, Pope Francis has been accused of appeasing Beijing and letting down Catholics in the underground movement who had not accepted the Chinese government’s interference, and who face the continued threat of persecution.

Deals struck between the Vatican and Beijing in recent years appear to have left a situation where the Chinese government appoints Catholic bishops, and the Pope gives in and recognises them. China says it’s a matter of sovereignty, while Pope Francis insists he has the final say – though that is not the way it has looked.

“He won't be pleasing everyone all the time, but I think what the Holy Father really wants to indicate is that the Church is not a threat to the state,” says Father Anthony Chantry. “He is treading a very careful path and it's fraught with difficulties, but I think what he's trying to do is just to build up a respectful relationship with the government in China.”

Rightly or wrongly, it is all in the name of bringing more people into the fold. Some of Pope Francis’ predecessors have been more uncompromising in many ways, seeming to be more accepting of a smaller, “purer” global Catholic community, rather than make concessions in either foreign relations or in the way the Church views, for example, divorce or homosexuality.