In his book, Dominion: the Making of the Western Mind, Holland uniquely straddles the world of secular intelligentsia and the phenomenon of Christianity.

Holland's own journey constitutes a surprise in itself. Fascinated by the drama and the power of the Roman Empire, he became an enthusiastic historian of antiquity. Rome captured his mind, but the suffering of the Yazidis at the persecuting hands of the Islamic State was what it took to break his heart.

As a historian he was only too aware of Plutarch reporting on the brutality of Caesar's conquest of Gaul. One million Gauls slaughtered in war; one million women and children carried off into slavery. Crucifixion was just the most dramatic display of raw power that the Romans used.

But when he visited the plains of Nineveh for a Channel 4 documentary in 2016, he came across crucifixion again. Islamic fighters had launched devastating attacks against the Yazidis, selling off nubile girl captives as young as eight as war brides, slaughtering the unattractive and crucifying the men.

Standing in a town called Sinjar where the men had been recently crucified was a game changer. No longer lost in the statistics and curiosities of history, no longer understood in the abstract, that most terrible form of execution became vividly and stomach-churningly real.

The rationale behind crucifixion was to celebrate indomitable ruthless power by those who had it at the expense of those who had less or none. Mercy and vulnerability were liabilities. The cross was a sign of humiliation, defeat, despair and impotence.

Standing amongst the bleached bones, broken bodies and tufts of hair of the dead Yazidi women and girls, Holland found himself "breathing in the dust of the air of a town where people had been recently crucified."

Suddenly he felt shame at the lack of curiosity and lack of historical empathy, and he asked himself what had changed since the Romans had practised their own sadistic political art of public strung-out and insupportable humiliation?

Part of the answer was that it was the symbolism of the cross that had changed. It had transformed a civilisation that celebrated the brutalizing impact of power into a Christian one that saw loving compassion conquer brute force.

It was the cross that had been transformed and changed its meaning. It became a symbol that declared the powerless triumphing over the powerful; the slave over the master; hope over despair; the victim over his torturer; life over death.

As St Paul initiated the inversion of what the cross stood for, he approached it from the viewpoint that the Jews would be unable to deal with the idea that the Messiah suffered and died, and that the Romans would dismiss any other interpretation of the symbol than failure. Slowly but surely the Christian narrative captured the mind, heart, imagination and soul of the West.

Holland points out that what was weird was not that Christians claimed Jesus was the Son of God; plenty of people believed that the emperor was the son of God. It was that the cross was a sign of the triumph of compassion and not failure; that inconceivably, the victim had more moral power than the wielder of brutality.

The thesis of his book Dominion is that Western culture has accepted the sanctification of the victim but has latterly come to ditch its belief or interest in Jesus. It has adopted the narrative of human rights as its new golden rule, but only because Christianity has persuaded the West that the individual matters; only because Christianity taught that each individual has the integrity of sanctity which flows from being created, redeemed and loved by God.

The West has forgotten why the individual has human rights, and therefore post-Christian culture faces the same dilemma as a man sitting on the branch of a tree while sawing that very branch off without realizing that it is his only attachment to the very trunk that holds him up. For all the self-confident protestations of humanism, and to the splenetic rage of Nietzsche, the de-legitimising of power by truth, love, and honour flow from the incarnation and the cross.

The question arises: can secular society retain the priority of the sanctity of the victim while repudiating the Christian teaching as to why the victim matters and replacing it with the supremacy of the group that progressive politics insists on? The answer will prove to be 'no.'

Can secular society protect human rights while refusing to believe that humans matter because God made them, and instead replacing that with believing you only have rights if you believe what the state tells you to believe? No, again.

Holland ended by asking what for many is the $64k question: what would it take to re-Christianize Western culture?

He answered his own question by insisting that it could only happen if society could be reminded of and persuaded by the truth that all it believes about good and evil flows from the Christian worldview.

It is no longer able to join the dots between the values it most treasures and the faith that gave birth to them. It is blind to the causal link between the two, and the simple truth that cutting the umbilical cord between the incarnation and the cross, and human rights and social justice will be fatal to the latter.

Perhaps, Holland suggested, if the Church were to rediscover its confidence in the strangeness of what it believes and re-encountered a commitment to the supernatural it might create a provocative gap between the secular humanism that is derivative of Christian values but has resisted the reason for them.

And it may be that this is the greatest challenge that confronts the Church. Holland lightly describes it as "recovering the experience and the authority to talk meaningfully and informatively about angels".

What he means by this is that the Church is the only agency that claims it has the experience and the expertise in a metaphysical reality that is not compressed into the materialism and empiricism of time and space. We might add that to the extent that the Church loses its confidence in the experience of the miraculous, the holy and the supernatural, it will have nothing to say that distinguishes itself from well-meaning humanism or "the kind of things that you'd hear on a Liberal Democrat party political broadcast", as Holland quipped.

He added that for him, it was his encounter in Iraq and staring the evil of the Islamic State's genocide in the face that helped him confront the deeper dynamics of good and evil.

He suggested that if the Western Church gave its attention to the sacrifice of Christian martyrs at the hands of their persecutors, it might reanimate the Church with the primal status of its unique message, which is why the words of Tertullian have always been true, "Plures efficimur, quotiens metimur a vobis: semen est sanguis Christianorum." We recognise this in translation as ,"The blood of the martyrs is the seed of the Church," which although less poetic, has greater impact in the more literal, "We multiply when you reap us. The blood of Christians is seed."

Dr Gavin Ashenden is a former chaplain to the Queen. He blogs at Ashenden.org