The shock of a Church deciding to bless sin has caused many evangelical Anglicans to re-think whether they can stay. Can they honourably serve God in an institution that some think has come close to the sin against the Holy Spirit? The blessing of sin is too close to the miscalling of good as evil and evil as good for spiritual comfort.

Three times in my life-time a crisis has caused evangelicals to reflect on whether they had in conscience to leave the Church of England.

The first was between Martin Lloyd Jones and John Stott in the 1960s. Lloyd Jones warned that faithful evangelicals could never capture the national Church for the Gospel. Stott insisted they could. Stott won the arguments and there followed a powerful evangelical renewal, launched by evangelists like David Watson, Michael Green and perhaps most famously Nicky Gumbel and his Alpha course. Stott was proved right.

There was another moment twenty years later, when a bishop of Durham, notoriously clumsy with his intellectually honed public conversations, questioned the veracity of the resurrection in public. At about the same time, some otherwise irrelevant theologians were publishing a book problematically called 'the Myth of God Incarnate.' But the bishop retired and the theologians slipped un-remembered into the shadows of time.

The coming of this present crisis might seem to be just one more struggle for the Gospel chronologically. Is the attack on the doctrine of marriage any different from the attack on the resurrection and incarnation of a generation ago?

Jill Duff, the Bishop of Lancaster, has been trying to steady the nerves of the conservative evangelicals by reminding them that they once had to put up with heretical bishops, and they weathered that crisis, so they can weather this one. But I believe that she is making a fundamental category error and that is because the new progressive values represent not one or two maverick officeholders, but a repudiation of the essentials of biblical epistemology.

Once you introduce a new set of philosophical ideas which are invested with the authority to re-interpret, redefine or ignore biblical principles, nothing authentically Christian remains safe or inviolate. And that is why I believe this crisis is of a totally different order.

Imagine for a moment the church as a block of flats. There is a noisy and anti-social tenant. He can't easily be expelled, but the landlord promises he is quite elderly and will leave soon. He does leave. His room is taken by a better behaved tenant. These things happen. Life goes on. Tenants, keeping or breaking the tenancy agreement, come and go.

But a new and different crisis arises: the building managers have decided to excavate under the building to expand it. They compromise the rules of safe engineering and do it badly. The foundations are damaged. The building is in imminent danger of collapse. No tenant is safe.

This is really about the creeds but not in the way people have imagined. The early Councils offered the Church the Ecumenical Creeds as an instrument for discerning the orthodox faith from heresy, they have served us well. Most of the arguments that mattered were about the Godhead, the perfectability of humanity and the nature of the Church. But the heresy that threatens the Church today is not an ideological one covering the same ground. It is an anthropological one over the nature of humanity.

The historic creeds did not address it. It was not their crisis. So to suggest that the present issues of sexuality is no great matter because it does not offend the historic creeds is a category error. Human identity and our relationship to our sexuality and sexual preferences was not on the theological map. But now it is. It has become a political issue with implicit theological and spiritual consequences.

Because this new anthropology presents itself as a political matter, too many people have been blind to its theological implications. The Biblical revelation that God made man and woman as two sexes in his image with the intention of heterosexual marriage with the principle purpose of having children is not directly challenged (for now). But it has been added to in practice. And it will eventually be side-lined by the adoption of this different, though eventually contradictory anthropology.

The biblical anthropology is in the process of being replaced by a secular and political one. Feminism and the accompanying ideology of egalitarianism has presented a competing and sub or non-Christian competing political anthropology. And it has been astonishingly successful. It has taken the society we live in by storm.

The Church was unprepared for feminism. It mistook it as a movement promising justice. It failed to notice that it carried a competing and contradictory understanding of the nature and purpose of our humanity and sexuality.

This was a devastating mistake. And it still hasn't been recognised for what it is by the politically liberal-minded in the Church - which constitutes a failure of theological perception being overwhelmed by political perception. In other words, the triumph of secular ideology over Christian discernment.

And we have now seen that there is a very serious trajectory of development. There is nothing to stop the ideological train of progress from moving from equality of value (which is the only principle of equality the Scriptures recognise) to equality of function.

The administrative management that has emerged in the Church over the last two decades is made up entirely of people committed to feminist principles and feminism is always going to lead to the normalisation of homosexuality because homosexuality and feminism have been like Siamese twins in the progressive value system. As a result we can see that the same-sex blessings that Synod has legitimised mark the triumph of the next stage of the progressive capture of the Church.

But the incorporation of feminism into the theology of the Church has had profound theological and spiritual consequences as well as political and economic ones. Feminism is a complex philosophical and political system of thought which has had several evolutions. Indeed, the whole highly charged 'Terf' wars reflect a civil war between second and third wave feminism.

Retrospectively the Church's approach to feminism was simplistic and ideologically naive. It mistook it simply as an instrument of equality. But with equality came also relativism; and with relativism and egalitarianism homosexuality emerged as being valued equally with heterosexuality.

The Bible might describe the practice of homosexuality as 'falling short', but feminist egalitarianism provided an alternative epistemology. It was declared not only to be of equal value, but in some terms superior, since it came with the cachet of victimhood. The values of secular culture had suddenly triumphed over biblical and theological culture. Some evangelicals suddenly noticed what was happening and protested. Others, more ineptly, simply adopted the new anthropology in the name of biblical justice.

But that was not the end of the new anthropological revolution. There was so much more to come. The next developments that follow inexorably are driven by the feminist aversion to fatherhood. They are setting out to replace masculinity with femininity or neuter terms.

The assault on all things masculine in our culture, the principle embodied by 'toxic masculinity', will be used (in contradistinction to the work of the Holy Spirit) to counter any ease or intimacy in the Church with God as Father. Yet, as C.S. Lewis so clinically observed, any change of pronoun to either 'she' or 'it' produces a very different god and a very different relationship with this different god.

Calling god 'she' has been the feature of the experiment in the worship of fertility religions (and more recently Gaia) - the replacement of creator with creation, which is idolatry. And calling god 'it' takes us down the road to Buddhism - exotic and enticing but mistaken. God is supremely personal.

We saw that the initiative to question the gender of God broke ground no sooner had the progressives succeeded with their determined attempt to legitimise same-sex blessings. What comes next? Once 'equality' applied to sexual couplings has established homosexual coupledom as an acceptable deviation from the Scriptural norm of one man and one wife, there are no reasons to oppose the inevitable implications for throuples – polyamory/ polyandry. The legitimisation of the sexualisation of children lies very close behind that and has already started.

It must be obvious that the 'difficult tenant' ineffectually and occasionally challenging the historic creeds and the compromised foundations caused by the emergence of this new anthropological creed, are not the same order of crisis. This crisis will cause first the disfiguring and then the collapse of any Church that fails to resist the new anthropological credal claims.

The problem for the Church of England has been intensified by growth of secular group-think. This has been sped up by the efficiency of the small body of people who became gatekeepers to senior appointments. They were devotedly secularised in their theological and political assumptions. For the last twenty five years they have pursued a policy of weeding out candidates from the episcopate and all other senior roles who gave greater weight to biblical and theological criteria than to the feminist and egalitarian ones. This highly effective policy was done with subtlety and efficiency. The promises of mutual flourishing were simply cosmetic, fulfilled by one or two totemic appointments of candidates who undertook to cause no trouble. This has resulted in a complete change of theological and spiritual culture at management level.

When prominent voices like the admirable Dr Ian Paul insist they need not leave because formal doctrinal statements relating to marriage remain in place and are backed up by the Thirty Nine articles, this mistakes the reality of the situation. The historic formularies remain in place only because the political muscle required to re-write them is, for the moment not there. But there is no evidence that conservatives have any power to stop or even slow down the inexorable tide of progressive change. The power of the new secular and egalitarian anthropology has such an impetus and potency that it has swept both through the nation and the Church, carrying many of the shallower evangelicals along in its wake.

There has been no sign at all that the authority of Scripture (backed by tradition) has the power to reconfigure the grip of this powerful secular conviction about the new anthropology. Anglicanism has always been more open to evolving rational ideologies than it has been committed to biblical principles. Rationalism has always managed to subvert Scripture. The progressive secular understanding of equality, justice, fairness and interchangability of the sexes is unstoppable in the West, and throughout the liberal Protestant churches. The C of E is simply one of the latest to succumb, as all the others have.

The fight against the new culture has moved to Catholicism, Orthodoxy and Pentecostals - unsurprisingly the churches which have retained a commitment to the supernatural and so have some epistemological resource to combat the presumptions of secularism.

Claiming that one can stay in a church as an act of fidelity to the Gospel when the church redefines sin as virtue and offers a cosmetic but distressingly inert blessing, is a lapse of discernment. It makes no more sense than if the musicians on the Titanic refused to leave the floundering ship because of their 'commitment to music'. A real commitment to music would involve taking to the life rafts and being saved to perform music in circumstances where it could be played. A real commitment to the Gospel would lead to finding an ecclesial home where the integrity of the Church needed fighting for and could be effectively defended.

Gavin Ashenden is Associate Editor of the The Catholic Herald and a former chaplain to Queen Elizabeth II.