It’s a sunny morning in London on the feast of Corpus Christi and, not coincidentally, I’m standing outside the presbytery of Corpus Christi Church waiting for someone to answer the door. Somewhat to my surprise, it is opened by the man I’ve come to interview: Cardinal Francis Arinze, who is in town to celebrate Mass. The former head of the Church’s liturgy department is marking the great feast of the Eucharist at a church named after it.

Cardinal Arinze regards me with the slight wariness of an ex-Vatican official meeting a journalist. But he’s in a good mood. He loves Britain, he says: “Whenever there is a good reason to come here – or excuse – I’m happy about it.”

His first visit was in September 1963, as a young priest working for the Nigerian bishops’ conference as education secretary for the east of the country. The bishops sent him to study at the Institute of Education in London. In 2005, when Arinze was widely tipped to become the first African pope in 1,500 years, the Times tracked down his old tutor Nick Evans, who remembered Arinze as a “sheer delight”, a good student who loved cracking jokes. Evans added: “I thought he would make a name for himself.”

From the start, Arinze’s exceptional gifts were obvious: when he returned to Nigeria he was made a bishop – at age 32, the youngest in the world. It was, he tells me, a formative time. He was “near the common man: the richer people in the big cities, the poorer people in the villages”. He had to speak clearly to those of every educational level – “and not engage in learned elucubrations above the heads of the people, just to show off that I have read many books, and people don’t know what you’re talking about.” He warms to his theme. “After Mass, you ask them, what did the priest say? ‘He spoke very well.’ What did he say? ‘I have forgotten.’ Because they didn’t follow it in the first place.”

Among Catholics, Cardinal Arinze is much admired for this kind of bluntness. Here he is on eternity (in a 2017 interview): “There are people who don’t want us to talk of hell. But hell is not something that was invented in the Vatican.” Or on being portrayed as a conservative: “Suppose you say that when we did arithmetic, we learned that 2+2 = 4. It’s still the same, so am I then ‘conservative’ for saying so?”

At other times he speaks the careful, precise language of a diplomat. On the difficult subject of migration, for instance, he speaks in cautious generalities. It’s a subject the cardinal knows from first-hand experience. On June 26 1967, he was appointed Archbishop of Onitsha, a week before the Nigerian civil war erupted. He was effectively a refugee, fleeing from one area to another as the theatre of war changed, while organising aid for the many displaced people. What did he learn from that experience? The cardinal generalises: “It is best for a person to stay in that person’s own land – country, town, area – and work there.” But sometimes, he says, that isn’t possible. And “in general, we cannot deny a human person the right to look for another area where you will have more peace, or even more study, culture or economic opportunity.”

Governments, he says, also have a duty to be realistic. “Each government has to see, for how many people can they provide? Not only their entrance: lodging, work, family, cultural insertion.” (One of the cardinal’s verbal habits is this kind of listing, as though drawing up a table of contents.) Moreover, he says, countries that lose their young people are losing the people who can build that nation’s future. “So the countries in Europe and America can sometimes help best, not by encouraging the young people to come to Europe as if they looked on Europe as heaven – a place where money grows on trees – but to help the countries from which they come.”

Leaders of countries with high rates of emigration, he says, should examine their consciences and ask why so many people are leaving. So should those who sell arms, which indirectly cause mass migration.

Some, the cardinal says, tell him this is “all theory”. The pitch of his voice rises. “It is not theory. It is fact.” For people who come to Europe: “Where is their future: work, family life, culture, religion? Think of all that.” He concludes this discourse: “So it’s all these considerations we must make, when we mention the word ‘migrant’.”

I begin my next question, but the cardinal interrupts. “But I must say: we must thank those who are kind to migrants. Those who welcome them. It’s what Christ would teach us, it is according to the Bible. Without forgetting the other considerations I mentioned.”

I suppose it needs discernment, I say.

“Yes. For all of us: government, society, Church, organisations.”

Shortly after John Paul II became pope, he picked Arinze to head the Secretariat for Non-Christians, later renamed the Pontifical Council for Interreligious Dialogue. Arinze worked with Muslims – a kind of dialogue he was very familiar with from pastoral work in Nigeria – as well as “Buddhists, Hindus, African traditional religionists, Bahá’í, Shintoists, Confucianists …”

In his 18 years in the job, he found that to really know somebody, you must understand their religious beliefs. “If you don’t understand a person’s religion, you haven’t even begun. And if you are not able to listen, you are only able to talk, then you are still on your own. You are lecturing everybody who comes near you, but you are not dialoguing with anyone.”

You may be surprised, he says, at what values you have in common with others. “There are some desires of the human soul which that other person is looking for. There are, maybe, mistakes in the way that religion is looking for those things. But the human heart, created by God, is looking for Him.”

Cardinal Arinze’s most senior role was as head of the Vatican’s Congregation for Divine Worship, a job he held for six years. His chief task was to meet bishops and priests, “read their letters, meet the lay people who come or who write – including those who exaggerate, those who have their own idea of the Church – and know how to say the correct word to each.”

The cardinal was seen as a conservative on matters such as priestly celibacy. It’s not a dogma, he says; nor is it compulsory in every part of the Church. “But it is a practice which has very good reasons. Christ himself, St Paul, St John … All along the corridors of history, you think of Thomas Aquinas, Robert Bellarmine, Don Bosco, the Curé of Ars who turned a parish that wasn’t worth the name into a beautiful parish. All that can’t be for nothing.”

Wanting to abolish celibacy because of the failings of some priests, he says, would be like banning cars because some people crash them.

“People appreciate it, also. Even in some parts of the world where the cultures allow the men to marry two wives, even in those areas they appreciate celibacy: both the sacrifice it means and …” – he slows down for emphasis – “the single-mindedness of heart which it indicates.”

Some people, he says, “those who don’t love the Church, or who have other reasons, may argue. But in their heart of hearts … You say to them: ‘Are you serious?’ ” He chuckles.

We’re at the edge of controversial territory here. Cardinal Arinze does comment on contested matters – for instance, those around the Eucharist. Last year he bluntly remarked, amid a controversy about intercommunion with Protestants, that you need to be Catholic to receive Communion. “After Mass, you can go to the refectory and have a cup of tea and even a glass of beer and a bit of cake. That’s OK. But the Mass is not like that.” The cardinal refrained, however, from naming any churchmen who disagreed with him.

Likewise, Arinze doesn’t mention the forthcoming synod on the Amazon, which will discuss possible exceptions to celibacy, supposedly as a solution to a shortage of priests. But when I ask him about the disparity of vocations around the world, his comments don’t seem completely unrelated. “The Church is Catholic,” he remarks. “We share. If one area of the world has not enough priests, let them look for another area where they can get priests. That is how missionary work is done.”

The cardinal was himself raised to follow a traditional African religion, but was baptised a Catholic aged nine. “I am sitting here now thanks to the Irish missionaries. If they had not come to Nigeria 100 years ago, I would not be a priest at all – perhaps not even a Christian. They sacrificed themselves, left their country, came to Nigeria to share the faith – where they didn’t know the language, where mosquitoes were rather active with malaria, and where roads were not excellent.”

So if one region is lacking priests, he says, we should “beg divine providence for happier days. But we must learn to share in the Church.” He refers to Pius XII’s Fidei Donum, which urges dioceses to be generous in sending missionaries. “Not a few dioceses are so well supplied with clergy, thanks be to God,” Pius writes, “that no loss would be felt if some of their priests should enter the mission field.”

I broach the doctrinal debates in the Church. Cardinal Robert Sarah – who, like Arinze, was once the world’s youngest bishop and now leads the Congregation for Divine Worship – said recently that the Church is going through a “dark night”. He remarked that “Every day I receive calls for help from everywhere from those who no longer know what they are to believe.” What does Cardinal Arinze make of that?

He leans back in his chair and looks at the far corner of the room, meditating on his answer. “If a Catholic says, we don’t know what we believe, or we don’t know what to believe … My response: there is a book called CCC. Catechism of the Catholic Church. That book has only 700 pages. You don’t have to read all of it at one sitting: if you read one page a day, you will be all right. That book is the best representation of our faith in our times.”

It’s based, he says, on the work of saints, popes, councils, traditions. “Buy a copy. If you don’t have a copy, sell your overcoat. You don’t need any overcoat – during the summer, at least.”

That brings us back to Corpus Christi itself, the feast day celebrating the Real Presence of Christ in the Eucharist. The key phrase, he says, is the one the priest utters after the Consecration: “The Mystery of Faith”. “Our faith is concentrated there. It is the gift of Christ to his bride, the Church, the night before he suffered; his way, his wonderful way, to remain with us so that we can pray and he will lead us. He is the chief person praying at Mass. He is the chief priest making the offering, at Calvary and at Mass. He is the chief victim offered, at Calvary and at Mass. The only difference being that at Mass he uses the ministry of the ordained priest, and that he does not suffer at the altar at Mass.”

Every Catholic, the cardinal says, should “strive to grow in knowledge of the Eucharist”, especially by attending Mass. “And in receiving Christ at Holy Communion, when you are well prepared. Every Sunday – every day, if you can – but always well prepared. This sacrament has all the other sacraments ordered towards it. It is the greatest sacrament.”

Dan Hitchens is deputy editor of the Catholic Herald