INSTITUTIONAL Christianity is in crisis about sexuality. Its detractors in the supposedly secularised and liberal climes of Northern Europe, who none the less yearn for what they call a satisfying "spirituality", see this crisis as a sign of its failure to engage the contemporary world.

Its conservative defenders, to be found mainly in religiously observant parts of North America, in Evangelical circles in Britain, and widely throughout the southern hemisphere, take it as an indication of cultural decadence and a deficiency in scriptural obedience.

I do not seek to solve the problems in the terms currently under discussion: "liberal" v. "conservative". Instead, I am attempting to go deeper: to approach the issue that is now called sexuality through a different route - that of the divine itself.

I write about God, and, more specifically, about the Christian God. I write for those who puzzle about how one might set about coming into intentional relation with such a God in the first place; and who wonder how - without sacrificing either intellectual integrity or critical acumen - one might discover this baffling, alluring, and sometimes painful encounter to require thematising in Trinitarian terms: "Father", "Son", and "Holy Spirit".

Further (and this may seem odd to the contemporary reader), I write in the fundamental conviction that no cogent answer to the contemporary Christian question of the Trinitarian God can be given without charting the necessary and intrinsic entanglement of human sexuality and spirituality in such a quest: the questions of right contemplation of God, right speech about God, and right ordering of desires all hang together.

They emerge in primary interaction with scripture, become intensified and contested in early Christian tradition, and - most importantly - are purified in the crucible of prayer. Thus the problem of the Trinity cannot be solved without addressing the very questions that seem least to do with it - questions that press on the contemporary Christian Churches with such devastating and often destructive force, such as questions of sexual justice, the meaning and stability of gender roles, and the final theological significance of sexual desire.

A PERCEPTION of the significance of the right ordering of desire was not, of course, alien to some of the greatest early Christian thinkers of the late antique era. A central part of my task is to explore how, for them, the perception of perfect-relation-in-God (the Trinity) was fundamentally attuned and correlated to their concomitant views about men and women, gender roles, and the nature of "erotic" desire.

Not that we can oblige any contemporary reader to accept their positions without critique (they are, in any case, various); but rather I seek, first, to lay bare the subtle -and forgotten - ways in which these elements in their thought connect, such that they may now illumine contemporary theological choices.

At the same time, it will become clear that the way they speak of desire has different overtones from today's post-Freudian context, and one as not yet cognizant of modern evocations of "sexuality". This difference is itself revealing.

Some of the most significant figures in the historical development of the doctrine of the Trinity (Origen, St Gregory of Nyssa, St Augustine of Hippo especially) feature large because of the fascinatingly different ways in which they relate their perceptions of intense desire for God, their often-problematic feelings about sexual desire at the human level, and their newly creative understandings of God-as-Trinity.

Yet the modern textbook account of the development of the doctrine of Trinity has largely obscured these crucial points of connection, often by concentrating more on philosophical issues of coherence, or political and ecclesiastical manoeuvring than on the Fathers' biblical exegesis or ascetical exercise.

It is not customary, therefore, to study the fourth-century Gregory of Nyssa's (fascinating) views about virginity and marriage while simultaneously exploring his contribution to the development of technical Trinitarian terms. It is not usual, either, to reflect on Augustine's understanding of sexual relations while studying his magisterial theological reflections on Trinitarian analogies.

But this omission is odd, not least because these two authors - prime progenitors of different, but mammothly influential, Trinitarian visions of the Godhead - themselves saw these points of connection, and discoursed upon them explicitly. And they did so under the impress both of scriptural injunction and of ascetic dictate, not merely by taking thought philosophically.

Both of them, too, had extremely sophisticated ways of insisting how God cannot be compared to anything creaturely (how a relationship with God is necessarily unlike any other), as well as a keen sense of how one's particular vision of God none the less also informs the whole realm of the personal and the political.

Once you grasp these nexus of association which they offer, you are also able to see, intriguingly, that their two Trinitarian traditions are not as disjunctive as they have long been presented. Here I contribute to a growing body of scholarship that seeks to reconsider the supposed gulf between early "Eastern" and "Western" views of the Trinity.

IN ADDITION to misrepresenting the Trinitarian developments of the fourth and fifth centuries, the standard modern textbook narrative has more fundamentally and fatally obscured much of the richness of the earlier, emergent stage of Trinitarian thought-forms in the first three centuries of the Christian era.

The picture here is more com- complicated than is the case with the Cappadocian Fathers and Augustine; because it must be admitted that polemical patristic authors of huge significance have themselves been strongly implicated in purveying the conciliar-based narrative that I am now seeking to query.

It is not just the story of councils and creeds and dominant ecclesial and political personalities to which one should attend in an account of developing Trinitarianism; and nor should the only principle of selectivity be a focus on an approximation to a presumed later "orthodoxy" (in the sense of assent to credal propositions).

By repressing or marginalising much of the early history of the doctrine of the Spirit (messy and erratic as it may seem), accounts of early Trinitarianism that give sole attention to the status of the "Son" vis-à-vis the "Father" up to the mid-fourth century miss much of the drama: at one and the same time, the crucial prayer-based logic of emergent Trinitarianism is missed, and the related and complicated entanglements with questions of human gender, power, and desire mutely disregarded.

I PROPOSE a rereading of the formative, patristic sources for the origins of the doctrine of the Trinity. I am also attempting to work out, in a number of perhaps unexpected and challenging ways, the issue of how such a rereading could creatively transform our current dilemmas about sex and gender.

My method of doing theology involves not only the primary practices of prayer and attention, but also an intensive multi-disciplinary approach, utilising fieldwork techniques and insights from the arts, alongside textual and philosophical analysis.

By the end, a vision of human desire, purged and transformed by ecstatic Trinitarian desire, becomes the means of recasting contemporary anxieties about "gender". Gender is now seen as less fundamental than desire for God (and thus as rendered strangely fluid by the interruptive workings of the Spirit, in Christ: see Galatians 3.28).

The same logic causes a rethinking of the relation of prayerful celibate and prayerful non-celibate vocations (as united in their commitment to Christ as the finaltelosof all desires: see Colossians 3.2).

What the world tends to see as "opposites" (a choice for sex vs. no-sex) turns out to be the wrong, disjunctive way of approaching the question in the first place. The crucial issue is the painful sorting of all desires (not just sexual ones) in the light of God's desire for us.

The key lies in a subtle shifting of thought in relation to practice: prayer, especially relatively wordless or charismatic prayer, becomes the means by which ascetic, ethical, and theological reflections are, in the long haul, reunited. Here, I argue, is the way beyond the false modern disjunction between "repression" and "libertinism" - a royal road in which the demands of tough, purgative asceticism and "infinite delight" finally converge.

The Revd Dr Sarah Coakley is Norris-Hulse Professor of Divinity at the University of Cambridge, and an Honorary Canon of Ely Cathedral.

This is an edited extract from her new book, God, Sexuality and the Self: An essay on the Trinity (CUP, £18.99).