Two weeks ago the Church of England's General Synod decided narrowly to approve prayers of blessing for gay (or in fact any unmarried) relationships. This may prove catastrophic for the Anglican Communion: bishops representing a majority of global Anglicans are speaking of a rupture with the bishops of the Church of England. Why, many observers from outside the Church will ask, can't they just agree to disagree?

The answer is that this isn't a minor disagreement about a peripheral detail of Christian practice. Rather, the heavy oak doors of the established church of the nation of England have come to enclose behind them not two different opinions about sex, but two entirely different religions. And they are not even similar religions; they are opposed at the deepest structural level. All that the sexuality issue has done is to force the difference to the surface.

Christianity is a religion about redemption. The Nicene Creed, recited weekly in churches across the world, says of Jesus Christ, for us men and for our salvation he came down from heaven. He came on a rescue mission: for humanity is a race gone wrong, ruined by sin, constantly inclined to do evil, and rightly facing the judgment of God. But God in his mercy sent his Son to earth to forgive us for what we have done, rescue us from what we are, and call us and transform us into true images of God in his perfect holiness. To achieve that required his total self-sacrifice for us on the Cross, and his Resurrection triumph over the grave. Despite variations in detail, this core of the faith is universally held by all Christians in all Christian denominations.

Or it was; until, the arrival of a German theologian named Friedrich Schleiermacher. Living at the end of the eighteenth century, by which time rationalism had made Christianity deeply unfashionable among the German intelligentsia, he came up with what he saw as a strategy for rescuing the Christian faith. 'If you have only given attention to these dogmas and opinions', he urged Christianity's 'cultured despisers', 'you do not yet know religion itself, and what you despise is not it. Why have you not penetrated deeper to find the kernel of this shell?'

His idea was that the universally-accepted doctrines of the Christian church were a mere 'shell' - ways of wrapping up and conceptualising what really mattered, which was a religious feeling. The feeling was the real thing; the shell was just packaging.

And so, all those things about Christianity which the modern world has made rather embarrassing - doctrines and miracles and ethical restrictions and the like - could simply be laid aside. Not discarded, for they were still valuable as (mythical) conveyers of deeper meaning: but now, like monopoly money, their value is in the experience that playing the religious game can give us, not in them having any worth in themselves. Religion can now be highly valued for its power for good in the individual human psyche and the collective human society, without awkwardly needing to insist on the truth of its unfashionable teachings.

Schleiermacher's proposal has divided the Christian church ever since. The established churches have in general welcomed it, for it shores up their position in an increasingly secular culture. They can keep their invitations to polite dinner parties, and join in the secular mockery of those poor gullible souls who still believe such things.

Meanwhile, orthodox Christians have seen it as nothing less than an abandonment of the faith.

Why? Because for them, Schleiermacher did exactly the opposite of what he claimed he was doing. It is not the shell of the faith he has discarded, but its kernel; not its outer clothing, but its beating heart. The doctrines of the Trinity, the Incarnation, the Atonement, the Resurrection and the coming New Creation are not mere foil wrappers to decorate the chocolate egg of a wordless religious sentiment within. Christ's death to redeem his people from the darkness and tyranny of sin is not a fiction to convey a religious feeling. These things are an account of reality, revealed to us by the one, true, creator God. To know them is eternal life. It is by them that we are saved. To demote them to a discardable shell is not to walk into the light but to plunge back into the very darkness from which Jesus Christ came to save us.

Besides, Schleiermacher and his followers, having relativised Christian doctrines out of the embarrassment zone, have not left doctrine as an unoccupied space. The human mind and heart, like nature, abhors a vacuum, and in orthodoxy's place Liberal Theology (as Schleiermacher's theological progeny came to be known) smuggled in other doctrines, less plainly articulated but no less real.

Schleiermacher held with his friends in German Romanticism (he shared for a while his Berlin lodgings with Romantic philosopher Friedrich Schlegel), a belief in the self and its motions as the source and origin of all truth. At the deepest level, this was a religion which valued man as the measure of all things: not a fallen creature in need of redemption and forgiveness by God his creator, but the omnicompetent master of the world, able to find within himself the resources to make sense of himself and the world around him.

God himself had changed from being our creator to something we created. And so he can and should be adjusted by us to help us make sense of and justify our experiences, longings and desires. The kernel of orthodox Christianity had been replaced by a very different religion.

Thus those claiming the name of Christian have been, since the beginning of the nineteenth century, functionally two religions. While many denominations have sided with one or the other, Orthodox or Liberal, in the Church of England they have existed in an uneasy truce. Liberals have mostly been willing to use orthodox liturgies – just as Easter egg manufacturers are still willing to wrap their chocolate in tin foil, though it is the chocolate, not the foil, they are marketing – because their words are for them an expression of sentiment, not statements of fact. So liberals and orthodox have been able to use the same services, prayers, blessings and hymns, though their core beliefs have been radically different.

Until now, that is. Because this awkward cohabitation simply cannot survive the importation of LGBTQ+ ideology into the church.

The reason is not hard to see. The kernel which the original Liberal Theologians imported underneath the shell of orthodox Christian language, was of course derived from the secular zeitgeist of their own day. For Schleiermacher, this was a viewpoint which desired in various ways a laxer application of Christian morality, but it did not seek to replace or oppose it.

But the zeitgeist has moved on. The centrality of the Self has mushroomed into a whole religious worldview, with its own deeply-held moral convictions. And this 'Progressive' religion – still embedded in the Church of England, and some other denominations – holds in many ways to a photographic negative of Christian morality.

Progressives see the union of gay couples as something that positively must be blessed; Orthodoxy sees it as a manifestation of exactly the indulgence of self from which Christ came to save us. Progressives see sexual licence as a mark of civilisation; Orthodoxy sees it as deeply destructive to ourselves and even more deeply dishonouring to a holy God. Orthodoxy sees human nature as in dire need of rescue from sin; Progressives see human nature as intrinsically good, and in need of rescue only from the prejudice of others. Orthodoxy sees goodness as defined by the holy commands of God; Progressives see it as defined by the freedom to satisfy the Self.

Yet more fundamentally, Progressives, in justifying why Christian doctrines must change, invoke the claim that we now know so much more about sexuality than Christ and his apostles did. But to the Orthodox, this is a denial that Christ is the omniscient God the Son in human flesh, the full revelation to mankind of God and his truth. Either Christ is God, and knows better than us; or we know better than him, in which case he cannot be God.

And so of course it is not possible to wrap up one in the clothes of the other. While the kernel of 18^th-century Romanticism could comfortably (as the theological liberals saw it) coexist with a husk of Christian doctrine and liturgy, a kernel of today's devotion to the Self simply cannot. The two are fundamentally opposed at too deep a level. Schleiermacher wanted to preserve Christian doctrine and its associated liturgy for its aesthetic beauty and the feelings it evoked. But Schleiermacher's heirs, the Progressives in the Church of England and elsewhere, now seek to shred it and replace it, because they consider it morally offensive to their core beliefs.

As a result, the era of the uneasy truce, sitting on two sides of the aisle in the same church, must and will now come to an end. Schleiermacher's kernel and shell can no longer be held together. The House of Bishops' attempt to bridge the gap by promoting prayers of blessing, but not marriages, for gay couples, was a demonstration of this. The Bishops claimed that they were not changing the Christian doctrine of marriage. But this was a lie, for that doctrine includes the imperative of sexual abstinence outside of holy matrimony, which the act of blessing unmarried couples entirely inverts. It was precisely this doctrinal change that the new liturgies are designed to achieve.

More substantially, it demonstrates how the House of Bishops has discarded the rest of Christian orthodoxy as well. What, in fact, is Christian faith anyway? The Orthodox answer has always hung on Jesus' words: Repent of your sins, and believe the good news, that Christ has come to forgive and transform into an image of God's holiness. Nonsense, say the Progressives; you are fine, and God will bless you, just as you are. Deny yourself, take up your cross, and follow Christ as Lord? No: what you must now turn away from is not your sins and yourself, but the belief that there is such a thing as sin and that there was ever any greater lord over you than your Self. Come in humble repentance for your proud heart before a holy God? No: pride is now the greatest of virtues, and Self is not to be sacrificed but celebrated.

Thus, in their 'Prayers of Love and Faith', the House of Bishops has blown apart the truce that has held for two centuries between Liberals and Orthodox in the church. As the tension between orthodox language and secular belief has reached breaking point, the bishops have sided definitively against orthodoxy and with secularism. That is the reason why Anglicans from around the world, who are overwhelmingly orthodox, have reacted with horror, declaring that the Anglican Communion can now no longer hold together. It is the reason why orthodox Anglican clergy and laity in this country are now openly talking about repudiating the authority of their bishops. It is the reason why other, orthodox, denominations such as my own will now find formal ecumenical relationship with the Church of England to be impossible.

Whether the Church of England will split, or one side will depart or capitulate, leaving the institution in the possession of the other, I do not know. Certainly both cannot remain in one organisation. Whether there will even be a Church of England in a few years' time, or what it might look like, is impossible to say. But if the ancient doctrines of Christianity, confessed by the orthodox for two thousand years, were never in fact mere wrappers for religious sentiment but a God-given revelation of reality, then there is no question that inside or outside England's established church, they will prevail.

Matthew Roberts is minister of Trinity Church York, and a former moderator of Synod of the International Presbyterian Church. His forthcoming book 'Pride: Identity and the Worship of Self' is published by Christian Focus Publications in March.