Justin Welby has a job which in political terms looks impossible. As Archbishop of Canterbury, he holds a grand and ancient office, but has virtually no power even over the Church of England, let alone over the other 37 provinces of the Anglican Communion, of which he is the symbolic head.

It is true that he has a pulpit. But how, when he ascends into it, or on other occasions, is he to find words which mean something to believers and unbelievers, and also to the many millions of people in this country who regard religion with indifference, and ignore, even at Christmas, our country’s Christian roots?

The Archbishop appears undaunted by these difficulties. As Charles Moore observed, on interviewing him at Lambeth Palace in the summer of 2013, a few months after his enthronement:

“Justin Welby is the fourth Archbishop I have met in this place; though new in the job, he is by far the most relaxed.” 

And although many of us ignore religion, it turns out that religion, or misunderstood religion, will not ignore us. One of the Archbishop’s roles is to explain this. He supports the bombing of Syria, but places it in a context which stretches far beyond politics. As he put it earlier this month in the House of Lords:

“The Just War criteria have to my mind been met. But while they are necessary, they are not by themselves sufficient in action of this kind – where we can end up doing the right thing in such a wrong way that it becomes the wrong thing… If we act only against ISIL, globally, and only in the way proposed so far, we will strengthen their resolve, increase their recruitment and encourage their sympathisers. Without a far more comprehensive approach we confirm their dreadful belief that what they are doing is the will of God… there must be a global theological and ideological component – not just one in this country – to what we are doing… And it must include challenging Saudi Arabia and Qatar, whose own promotion of a particular brand of Islamic theology has provided a source from which ISIL have drawn a false legitimisation.”

Victory, the Archbishop remarked in another recent speech, “will mean the end of religiously motivated violence”, of which the Christian-generated version ended in Europe with the Peace of Westphalia in 1648. He added that “the present conflict must be won for faith of any kind to have any reputation in the public mind.”

All this sounds, and is, highly serious. But it is striking how often the Archbishop tells jokes. For example, in a recent speech to the General Synod:

 Many of you will remember the performance of Kenneth Williams in “Carry on Cleo”, in which, as he faces his murderers, he cries out, ‘Infamy! Infamy! They’ve all got it in for me.'”

In dealing with Church affairs, a sense of humour is pretty much indispensable if one is not to be driven mad. The Archbishop was trying here to warn against the partisan, or tribal, spirit according to which in every dispute one thinks the worst of one’s enemies, and is convinced they are trying to do one down.

Justin Welby is careful not to attach labels to people, including himself, and has adopted a new approach to the dispute within Anglicanism about homosexuality, which has pitted American liberals against African conservatives. Instead of trying, almost certainly in vain, to devise a doctrinal formula which can encompass both groups, he proposes that they remain in communion with Canterbury, but not necessarily with each other.

A Lambeth Palace source told Andrew Brown, who writes on religion for the Guardian, that the Archbishop did not wish to leave his eventual successor in the same position of “spending vast amounts of time trying to keep people in the boat and never actually rowing it anywhere”.

When Brown asked whether this solution represented, if not a divorce, a legal separation, a Lambeth source said: “It’s more like sleeping in separate bedrooms.” Which in some upper-class households is normal practice, and perhaps helps to ensure a better night’s sleep.

Justin Welby’s own background is highly unusual. His parents’ wedding reception was held at 11 Downing Street, for his mother, Jane Portal, was the niece of Rab Butler, who was Chancellor of the Exchequer, and might have become Prime Minister.

Here was an initiation into the ruling class. The Butlers had helped run the British Empire: Rab’s early ambition was to become Viceroy of India. And as Justin, born in 1956, recalled when he appeared on Desert Island Discs:

“I remember my mother taking me to tea with her former boss, who was Winston Churchill – she worked for him for six years [as secretary during the Second World War] – a very, very old man, and he cried, and because he cried, I cried, and then we sat and had tea.”

But the marriage of Justin’s parents lasted three only years. He had a miserable adolescence, caring for his father, Gavin Welby, a gifted fantasist who had declined into alcoholism and poverty. Justin recalled idyllic visits to his mother in Norfolk, but an “utterly insecure” childhood with his father in rented flats in London, doing a “moonlight flit” to escape from creditors. He spent a Christmas alone with his father, who did not get out of bed: “That was a grim, grim day.”

After Gavin’s death, he turned out to be eleven years older than he said, and to have been born Weiler, the son of a German Jewish immigrant, rather than Welby, a connection of the Lincolnshire Welbys.

Justin was sent, at his father’s wish, to Eton, which waived the fees for the last two years. He was a contemporary of Charles Moore, who wrote after meeting him again in 2013:

“I am amazed. I first saw this man 40 years ago, when we were both pupils at Eton. Later, I was with him at Trinity College, Cambridge. He was the shyest, most unhappy-looking boy you could imagine. Now he is 105th in the line that began with St Augustine. He seems to be loving it. I remark on the change, and he agrees. ‘That’s something to do with the Christian faith,’ he says.”

While an undergraduate, Justin’s life was transformed by the personal conversion experience which turned him into a devout evangelical Christian:

“in New Court, Trinity College, during the evening of October 12, 1975…praying with a Christian friend, he suddenly felt “a clear sense of something changing, the presence of something that had not been there before in my life. I said to my friend, ‘Please don’t tell anyone about this’, because I was desperately embarrassed that this had happened to me, like getting measles.”

He met his wife, Caroline Eaton, at Cambridge. For 11 years, he pursued a successful career in the oil industry, at first in Paris, and here the Welbys suffered the deep affliction of the death of their oldest daughter, Johanna, at the age of seven months, in a car accident. They have five other children, who are now grown up.

A week ago, Justin Welby preached at Child Bereavement UK’s Christmas carol service at Holy Trinity Brompton church in London. He began:

“There are two prayers that many people here will have prayed. Anyone who’s lost someone in an untimely way, particularly perhaps a child, sibling or parent, very close friend…. One is, ‘Make them better. Lord, make them better. Get them out of this. May they recover and be healed.’

“The other is when that prayer has passed. A lot of people pray, ‘Lord, let me join them. Take me as well.’ The fact that we’re all sitting here today is because, for many of us, neither of those prayers were answered in the way we hoped.

“But time goes by and we begin to rebuild our lives. We never ‘get over it’  –  that’s such an atrocious expression  – but we do begin to rebuild. You live with this gap, as Caroline and I did more than 30 years ago when our eldest daughter died, and you begin to rebuild.”

For Justin, the rebuilding included the decision to become, after increasingly close involvement with the thriving, evangelical form of Anglicanism which developed at Holy Trinity Brompton, a priest. He read theology at Durham and spent 15 years in the diocese of Coventry, the last five at the cathedral, where he was much involved in reconciliation work, some of it perilous, in Africa and the Middle East.

In 2007 he became Dean of Liverpool, in 2011 Bishop of Durham, and after little more than a year, he was chosen as Archbishop of Canterbury. This latter phase of his career may fairly be described as meteoric. But although he expresses surprise at this turn of events, and seldom misses a chance to make a self-deprecating joke, one cannot say he looks disconcerted.

He is a part, however inadvertently, of the renaissance of the ruling class to which his mother’s family belonged. An underestimated aspect of being educated at Eton is the parental ambition which is there declared. Justin Welby’s clever, wayward father wanted him to do well, and in an unexpected way he has fulfilled that hope.

He has risen to high office, and has the presence, the readiness to finesse intractable difficulties, one might almost say the sangfroid, to carry off the task of representing 80 million Anglicans (the number the Communion claims for itself).

At a recent appearance at the Council on Foreign Relations in Washington DC, Welby observed that “the average Anglican is an African woman in her thirties, living in sub-Saharan Africa on four dollars a day”. He added that in many African countries, when the local Archbishop says something, “people tend to do what they’re told”.

In England, by contrast, they regard what the Archbishop has to say as “an interesting suggestion as a starter for discussion”. Justin Welby smiled, and for a moment his body shook with laughter at the thought of his own ineffectiveness.

Yet by acknowledging his powerlessness, he seemed liberated. He had admitted something which a democratic politician, striving for office, would find harder to admit. Perhaps – it is a possibility canvassed in II Corinthians 12, and proclaimed by the birth of a baby in a stable – his strength is made perfect in weakness.